Tactical Technology for TEOTWAWKI – Part 6, by J.M.

(Continued from Part 5. This concludes the article series.)

Pilot of the Airwaves

Another area where mobile electronics can provide some useful tactical functionality is communications, even if cellular networks and the Internet aren’t available. There are a lot of good articles here on SurvivalBlog.com about radios, so I’m going to focus on other areas.

One very useful option for communications is a goTenna Mesh paired with each mobile device on your team. They’re around $180 a pair, but goTenna frequently has them on sale for 20% or more off. It’s a small device that you clip to the outside of your gear and pair with your mobile device using Bluetooth that allows you to send text messages to other goTenna users. It uses MURS frequencies (151/154MHz) to communicate between goTennas, and all communications are strongly encrypted. They advertise up to a 4 mile range between devices in the open, and I’ve been able to exchange messages with another user over two miles away through broken terrain; there are even stories of people being able to connect over a distance of 25 miles in perfect conditions.

Being able to exchange information via text messaging can be a huge advantage if you need quiet communications in tactical situations, and there’s a lot less chance of your communications being intercepted than with radio. There are also instructions available on how to make your own solar-powered goTenna repeaters, which you could deploy on some high points around your AO to extend your range – the goTennas will ‘hop’ a signal between devices to get it to its intended recipient. Once the goTenna app is installed on your device, no Internet access of any kind is required to communicate with other users. Note that goTenna provides an optional subscription service called goTenna Plus, which allows you to do things like download and use topographic maps to share your location, have messages relayed via cellular service when one user in the mesh has cell service, automatically send your location to someone at a regular interval, etc. These options are pretty nice, but since they require Internet access and GPS so I wouldn’t recommend counting on them in a post-SHTF scenario.

One of the limitations of goTenna is that the MURS frequencies it uses restricts the amount of data that can be transmitted. This is why the app is limited to only sending text messages. There are other app-only options for communicating between mobile devices when the Internet is not present that provide a less expensive solution than goTenna, but most of these utilize Bluetooth and/or WiFi on the device itself, which is going to limit the effective range. The upside is that WiFi and Bluetooth provide much higher data bandwidths, which means you can send things like photos, and files, and even make voice calls. Here are some options:

Some of these apps support WiFi Direct, which involves directly connecting two mobile devices point-to-point via WiFi. Others require a WiFi infrastructure network be present, which you could create using the field WiFi network I mentioned earlier. I’ve played around with several of these and they all have their strengths and weaknesses. If goTenna isn’t a viable option for you or you want the ability to send things like pictures back and forth between mobile devices, I recommend trying out some of these other apps to find one that meets your needs.

Another function that a mobile solution can help out with is the ability to intercept and record radio communications when you’re out in the field. For example, say you’re monitoring an area and you notice some suspicious-looking characters talking to each other on what look like cheap Wally World FRS radios and you’d like to listen in, but you’re carrying Motorola MURS radios for your team, which don’t get FRS frequencies. You can plug a RTL-SDR ($25) dongle into your mobile device using an OTG adapter, hook up an antenna, start the SDR Touch app and start scanning. For those of you that aren’t familiar with it, SDR is Software Defined Radio, and it’s a small device that plugs into a USB port and uses software to perform most of the functions performed by hardware on traditional radios.

With the appropriate antenna it’s capable of receiving radio communications on frequencies between 500 KHz and 1.2 GHz. While originally used on PCs, Macs and Linux computers, some enterprising folks have created an Android app called SDR Touch that allows you to perform most of the same functions that you can on a PC. You will need an OTG adapter to plug it into a mobile device, and I recommend using one that allows you to supply external power so the RTL-SDR isn’t draining your mobile device’s battery.

The antenna you use is going to play a big role in how well you will receive the desired radio signals on your RTL-SDR, and the one I recommend is a Multipurpose Dipole Antenna Kit ($15), made by the same folks that make the RTL-SDR. It’s lightweight and breaks down for easy transport, you can adjust the length of the antennas to optimize for frequencies between 70MHz and 1030MHz, and the base has a standard ¼” screw hole, so you can mount it on the tripod selfie stick I mentioned earlier (hint: bring a small tape measure to get the antenna lengths right). Other portable scanning antenna options include:

If you’re not familiar with the RTL-SDR I highly recommend reading the book ‘The Hobbyist’s Guide to the RTL-SDR: Really Cheap Software Defined Radio’ – it provides a wealth of information on how to use and optimize the device. There are also some other useful apps that can help when you’re scanning – Antenna Tool can help you figure how long your adjustable antennas need to be for a specific frequency, and US Amateur Radio Band Plan which can help you remember what the various radio frequency bands are.

You could also use mobile radio systems like the RTL-SDR for radio direction finding to locate someone transmitting with a radio, but it requires additional equipment and expertise – check out this and this.

Sound Off!

While humans rely heavily on visual cues, sounds can also play an important role in awareness and information gathering when in the field, and there are some electronic technologies that can improve your ability to collect and manage sounds. The first and most obvious are hearing amplifiers like the Walker’s Game Ear and Walker’s Silencer. Both of them amplify available sound, and both provide some protection from loud noises like gunfire. You could also use standard electronic ear muffs, most of which also amplify sound, but they’re kind of big and bulky for regular use. A regular hearing amplifier works to amplify ambient sounds, but most won’t provide very good protection from loud gunshots. The ‘As seen on TV’ SuperEar Personal Sound Amplifiers works surprisingly well, but the downside is that you have to hold it and point it at the sound source you want to amplify, so it’s better suited for listening when you’re staying in one place as opposed to being on the move. An advantage of the SuperEar is that it provides an audio-output jack, so you could pipe the sound into your mobile device or voice recorder and record what you’re listening to. If you want to both listen and record at the same time, you can use an audio splitter to plug in both headphones and a cable for your recorder.

If you want to be able to pick up sounds from a long distance away you’ll need something like a parabolic microphone, which uses a dish to collect and focus sounds. Unfortunately, decent parabolic microphones are bulky and expensive, so they’re not very practical for normal field use. Keep in mind that with parabolic microphones, larger dishes tend to pull in sounds from further away, so bigger is better. A company called Telinga makes a parabolic dish that rolls up for easier transport, but the disk alone costs $200 with shipping. Of course you could always go with one of those kid’s spy microphones, which I’ve never tried, but it’s gotten some surprisingly good reviews on Amazon. If you want to roll your own just search the web for ‘DIY parabolic microphone’ – there are tons of examples available.

Another possible use case for audio equipment would be recording when you’re not present – say for example there’s an abandoned house that looks like it’s being used by squatters, but there’s no one around and you don’t want to set up an observation post to watch it overnight. You can plant one or more tiny voice-activated recorders around the rooms being used, then come back the next day and access what was recorded using your mobile device. Alternatively, you could plant some FM or FRS/GMRS frequency wireless microphones and set up nearby to listen in on what’s being said. I realize that some of this sounds like it’s straight out of a spy novel, but depending on your circumstances and AO it could prove to be useful.

Dammit Jim, I’m a Doctor!

Another area where electronic technology can be leveraged is for medical care – in addition to the medical-related reference apps I mentioned previously, there are several options that can help you diagnose and monitor medical problems in the field. The simplest one is a magnifying app on your mobile device, which provides some limited macro zoom capabilities for your device’s camera. This can be useful for finding splinters, ticks, etc., particularly for those of us with more ‘mature’ vision.

The new generation of inexpensive ‘smart watch’ devices provide the ability to monitor a person’s blood pressure, heart rate, body temperature and blood oxygen level with a single device, and many of them provide a Bluetooth interface which would allow your medic to monitor a person’s vital signs without having to stop and take readings or remove their clothing in cold weather. I’ve used one of these for a couple of months, and most of the readings it provides are surprisingly accurate; the one that always seems to be a few points off is blood pressure, but it’s consistently off so I can easily adjust. One recommendation is to put it on so the sensor is facing the inside of the wrist near where you normally check for a pulse, as this seems to provide the most accurate readings. They also have to be worn for a while (10-15 minutes or so) before they start providing accurate readings for temperature.

An otoscope is a potentially useful medical device – it’s basically a shorter version of an endoscope with a stiff handle on the camera end that plugs into your mobile device. This can be used for looking inside the mouth, ears, etc. to check out problems or wounds. This is probably more useful in your home medical clinic, but it might have some value on longer trips out in the field.

You may also want to consider a portable ultrasound machine. Note that these are expensive (anywhere from $1,300 to $10,000 and up) and require some training and experience to use effectively, but they’re great for checking for broken bones, finding foreign objects in soft tissue, etc. The US military started deploying portable ultrasound machines to their SpecOps medical teams many years ago, with extremely positive results. There are a number of good books and videos on YouTube on how to use ultrasound machines, and yes, I realize that watching some YouTube videos won’t make you a doctor, but you have to start somewhere.

Odds ’n Ends

There are a lot of other miscellaneous technology solutions that can be useful for field situations. One of these is motion detection, which allows you to check for people coming down a trail, or allow a single watch stander to monitor multiple possible approach paths. One motion sensor I’ve used for monitoring possible approach paths during paintball games is battery powered, connects to a WiFi network and sends alerts to your mobile device, so you’ll need to set up a field WiFi network in order to use these. A company called Olymbros makes a very cool outdoor wireless motion detection solution that doesn’t require WiFi – the sensors send alerts directly to a watch you wear. I don’t have any experience with the Olymbros product, but it’s on my wish list. Note that the sensors use 9V batteries, so you’ll need to include a couple of rechargeable ones in your preps.

One thing I’ve done that works well is to stick one of the wireless cameras I discussed earlier on the bottom of a motion sensor, and connect to the camera when I get a motion alert to see what triggered it. A note about motion sensors – since they detect changes in temperature moving across their field of view, one of their biggest issues is that you tend to get false alarms from moving shadows, blowing branches, etc. One thing I’ve done with the ones on my house is to glue a short piece of plastic tube over the round sensors or flat plastic ‘blinders’ to the side of the horizontal ones to limit their field of view, which significantly cuts down on false alarms.

Technology can also help you locate things like hidden caches. I have a couple of the Tile Mate Pros that I attach to various pieces of equipment that tend to walk off around our house, and I’ve got a couple more in my prep kit. Note that the Tiles have a feature called Community Find that allows you to locate things if someone else with the Tile app has passed near it recently, along with the ability to locate something using directional finding with Bluetooth from up to 400’ away (for the Pro). Having other folks potentially know where your caches are located probably isn’t a great idea, so I have a couple of these that I’ve paired with my phone and store in a Faraday Box. I figured they’ll be good for marking caches post-SHTF when cell service and the Internet are gone, using the Bluetooth find feature to precisely locate them. They use 2032 batteries that are supposed to last up to 1 year in the device.

Remotely triggering things is another possible application for technology. I’ve played with both WiFi and Bluetooth controlled relays, and by hooking up an electric match and battery to some fireworks I’ve created a remote fireworks controller. Note that the WiFi one needs to be connected to a WiFi network, and the Bluetooth one is limited to about 30’, so neither is a great solution if you need to be further away. In that case I recommend you consider some standalone wireless remote relays, which use a lower frequency and have a much greater range, even through obstacles.

There are lots of other possible applications for technology that can help if you’re out in the field, making your way in a TEOTWAWKI world. A few more ideas are:

  • Range finder – For some reason I’m lousy at estimating ranges.
  • Handheld weather station – For keeping track of changing weather conditions.
  • Air quality monitor – This would be useful if you’ll be operating near any potential sources of dangerous chemicals.
  • Casio sensor watch – Besides being a great solar-rechargeable watch that’ll last for years, it includes a compass, barometer and thermometer.
  • Portable Lightning Detector – If you live somewhere that gets frequent severe thunderstorms, this could save your life.
  • Electronic lighter – These can be recharged via USB, and some even come with a flashlight.
  • Geiger counter – If you live within a hundred miles or so of a nuclear facility, or you’re concerned about nuclear war.

And finally, the electronic gift for the prepper that has everything when money’s no object – a Boston Dynamics Spot Robot to help carry the load – only $74,500!


I’ve covered a lot of different technology options, so some of you are probably thinking that there’s no way you could afford, carry or use all of these things, and I’m not suggesting that you do so. My goal for this article was to provide some information on various technical options that could increase your effectiveness when you’re mobile in a post-TEOTWAWKI world, and as always you should start with understanding what scenarios you’re concerned about, what your area of operations looks like, what you plan on doing and how you plan on moving around. Once you’ve got a handle on those you can begin to understand how you may be able to apply the appropriate technologies to improve your effectiveness in the areas that are most critical to you. At a minimum, I’d recommend that you start by looking at what you may already have (like a cell phone) and how you could use it in a post-disaster scenario, then expanding from there. I’ve only scratched the surface of some of the technologies you could use, so if you have any other ideas or suggestions please share them in the comments.


  1. This would have to be one of the most useful and enlightening series of articles I have read. I am in Australia and a lot Prepper articles don’t apply here this one was very informative and although I am a technologist by profession I gained a lot of very useful information from this article. Many Thanks

  2. Outstanding article J.M. Lots to think about and investigate. Obviously real world results will vary so a solid scratching of the surface of the many options available is greatly appreciated.

    I once read (ok 5 times now but whose counting) a really incredible series of novels by a guy named…. J.. Jams no no it was James somebodyoranother. It doesn’t matter, they included a great deal of information on using a combination of High and Low Tech solutions by a whole bunch of interesting people

    I forget the exact titles but I think they were: Pickles, Souvenirs, Librarians, ExtraCredit, and Flounder. 😉 I could be off on these, you better check

  3. This is a well done, quick overview article of available technologies. It has my gears turning to see what I might could do/use to improve my prepping. I really appreciate the many links that a lot of articles are lacking. Thanks for sharing your knowledge.

  4. Hi J.M., this was a very informative series. It took 90 minutes to get through each day’s section due to clicking on all the links to check out the possibilities. That was an education in itself. And I finally got off my keister and got some rechargeable batteries ordered and put the electronic lighter on my next-month list while I’m digesting the rest.

    How good is the resolution on the magnifying app? I currently just use the camera on my phone, take a pic and then zoom in so I’m wondering how much better the app is. Even with glasses on, I can’t read some of the super-fine print on very small electronics like the 12 v cigarette lighter charger in my truck so I take a pic and zoom in. Ditto for those yellow shelf stickers at the store when you’re trying to read the finer print or it’s too low to the floor to see without laying down in the aisle. Someone’s liable to start CPR if I do that.

    Thanks again for all the time put into writing this article and all the useful info!

  5. St. Funogas – Thank you. Re: the magnifying app – it’s OK, but how well it works depends a lot on your mobile device’s camera, lighting, etc. I’d recommend downloading a couple of different apps and trying them out to see which one works best for your device.

  6. Hi guys, seen your traffic on the DIY wideband antenna into our Apollo-NG wiki. I’m also very focused on post SHTF networking and currently working on some prototypes for LoRa mesh based communication, where we have little devices bootstrapping a LoRa Mesh and offer BT LE interface for a smartphone app. Completely grid/cell infrastructure independent.

  7. Here is a problem that no one can explain: I travel and hike and when I’m at the Grand canyon my cell phone get’s no service. I complained to AT&T because I could see other people using their cell phone. AT&T claimed that my service was not blocked or limited in any way. So I changed providers and now I can get cell phone service (same physical phone) at certain places on the South Rim. But yet I have seen people walking a mile down the trail from the rim carrying on a conversation on a cell phone where there is zero service. Is it the phone, the carrier, extra cost service, what? This is a common problem in a lot of remote places but in the Grand Canyon there are a couple thousand people around and you are far more likely because of that to actually see the difference. That is where you phone gets zero service and others have normal service. I have had the same thing happen to me on the Pacific Crest trail, for example, where suddenly my cell phone starts working where it wasn’t for the last 20 miles or so. The difference I see no one else on the trail so I don’t know what others experience is. But the Grand Canyon experience exposes the problem clearly. So what is the answer? I partially fixed it by changing providers but others are still getting normal service in truly remote areas. Why?

  8. OneGuy – there are dozens of factors that can impact the quality of your cell signal – the terrain between you and the closest cell tower, weather, signal interference, the radio implementation in your phone, etc. There’s a web site call cellmapper.net that will show you where towers are located for each provider, along with some signal strength values for various areas. There are also apps like ‘Network Signal Info Pro’ that will provide a ton of cell signal info directly on your phone. With these you can start to get a better idea of what’s actually happening in terms of your phone signal.

    1. And I do understand what you are saying. But with AT&T we could stand beside someone using their cell phone and our’s showed no service. Then when we changed to Verizon we could stand in the same spot as before and using the same phone and get service. AT&T was blocking our service. Also, the strange case of the man walking into the Grand Canyon a thousand feet below the rim talking like he was downtown. NO ONE get’s service over the rim. My point isn’t to simply complain, what I’m saying is something is going on that isn’t being revealed to us. There are two factors in play: 1 is that even when there is sufficient service your provider may block you. Why? I have no clue. 2. In some places, like over the rim, you aren’t in line of sight to a cell phone tower, “no one” gets service down there, except some people do. I should have stopped the guy and asked him who his provider was or what kind of phone he used or some explanation for why he got service. This is a tech thing, someone knows the answer.

    1. In the case of the man below the rim it was clear to me he was talking to his work. He was getting briefed on problems and telling them what to do. I suspect he was from L.A. or Phoenix on vacation. Most of the other examples, those above the rim but in areas we did not get service, were woman just chatting and it did not appear to be walkie-talkie.

      If we had never changed providers and then got service in these areas I would still be believing my AT&T rep who swore that there was simply no cell phone service there and it had nothing to do with any corporate decision. My best guess is that AT&T does not own the nearest tower and prefer to show “no service” on their phones rather than pay the tower owners for the use of their equipment. My second guess is that is we had purchased their most expensive plan that magically cell service would appear in the same location.

      One twist in this story is that my wife changed her provider from AT&T I did not. We did that for a reason. She likes to use the phone and gets and makes calls all the time. I rarely use my phone but when we travel I use it to ‘tether’ wifi for my laptop and my AT&T service is unlimited so I can connect as much as I want to (except at Grand Canyon).

  9. @J.M.- Muchas Garcias ! (LOL) Very useful articles. I have archived them for future reference. And thanks to James or whoever at SB who recognized their worth and posted them.

  10. Thanks, James, for the heads up on the Enfield book. I must have it.
    In 1974, while attending New Mexico Military Institute, I spied an obscure door in the mess hall, which doubled as a study hall. No one ever used that door. So I did.
    it revealed a spiral, stone staircase leading deep down into a dungeon. In the vast dungeon, were rows and rows and rows of bookshelves, with a huge, clear light bulb every 100 feet. Holy cats! New Mexico’s Smithsonian, thought I. I found this huge, thick, dusty book about the history of the SMLE rifle. Like, Chicago white pages thick. Ancient drawings, specs, history of the development and evolution of this fantastic rifle.
    History of notable deployments and huge battles on the Dark Continent. Of battles between 6,000 British troops, armed with the new rifle but using the old black powder, 215 grain round nose load, at ranges to 2,000 yards in volley fire as tens of thousands of warriors stormed down a vast slope. Three ranks, 1,000 riflemen each, rained 20,000 rounds per minute in on the charging mass, starting at 2,000 yd. By the time they reached 700 yards, the carnage was obvious and the enemy ran back up the hill, sustaining horrible casualties during withdrawal.
    Since I owned a Number 1 MK 4 at the time, I read this huge book for weeks, which may explain my lackluster math grade.
    But make no mistake, the most under-rated battle rifle in gun stores is the SMLE, .303. A few FTRs (Factory Thorough Repair) are seen now and then. I bought two in the 1990s for $125.00 EACH. Brand new barrels. Very good stocks. Shiny, thick, brass butt plates. Long Branch arsenal. Ladder rear aperture sight graduated to 2,000 yards.
    I have often regretted not procuring that book back in the day. Probably wound up in a landfill.
    And so, when you see those Mausers and other early modern battle rifles with those large yardage figures stamped on the rear sights, you know what that’s for. Massed, volley fire.
    For those out there with .303s, plain vanilla .308″ bullets shoot just fine in them. You might use a .308″ expander ball on your resizing die, or remove it all together and the neck tension will work fine. I’ve shot some very nice groups with .308″ bullets in an SMLE, which is supposed to get .311″ bullets. Sierra makes a dandy 174 grain match bullet for it.
    If I recall, 42.0 grains of H4895 and a Remington 9 1/2 primer using a 165 grain .308″ bullet works peachy. But please check your manuals. It’s been a while since I loaded for .303.
    While in Canada for a time, I quizzed Canadian gun people about calibers they preferred for moose, elk. “You Americans. .30-30 Win, .30-40 Krag, .303 British… works FINE. BANG. Moose tips over. We go home.”
    I once shot a whole case of 1926 Mk VII surplus ammo through an SMLE. Every single round went off, and every single round split the case neck due to embrittlement. Sometimes, though, old Cordite propellant can absorb moisture, and produce long wait times on hang-fires. Like, two seconds. I have a case lot of Egyptian Mk VII that does this. So I’m just pulling the bullets, replacing the propellant, and reseating the bullets.

  11. Loved the direction of the article. I’ve been playing around with some motion sensors, and I would like build them to broadcast a unique tone on FM to signal traps. I’ll be publishing the diagrams once they are done and offering them for sale.

  12. Thanks for this series of articles. I’m an electronics engineer and ham radio operator, but there were so many interesting things in this series that I’d never seen or heard of. Thanks so much.

    On texting with phones– There are small battery-operated Bluetooth TNCs that can be used with an APRS app on the phone, and plugged into a handheld radio like a Baofeng. This is another off-grid texting solution/ If you’re a ham radio operator, you can use the standard 144.390 APRS frequency, but if not, perhaps a MURS channel would work.

  13. I’ve been wanting a tech gadget that none of my tinkering friends seems to want to tackle. I’d like a solar powered motion detector that triggers an inside device that plays a barking dog. The Cadillac version would have more than one detector and the barking dog would sound like he was moving from room to room.
    Yeah, I know that’s letting the peeps get close to the house, but I live in suburbia and don’t have much choice right now.

  14. Nurse kim – The WiFi motion sensor that I mention in the article could be rigged for solar power (it uses 3 x AA batteries), and it works with IFTTT so you could rig something that triggers a dog barking sound.

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