(Continued from Part 3.)
The second type of alerting – remote signal back to a centralized alarm console with a wired or wireless connection when the tripwire is tripped – can be a bit more complicated. In either case you can use something as simple as the clothespin switch to connect two wires to close the circuit, or to ‘press’ the button on a remote transmitter to trigger a relay that set off a light/buzzer.
Regardless of the use of local versus remote alerting, if there are any electronics or other components that could degrade when exposed to the elements (like primers, flares, etc.) used in your alerting device you should protect it. This can be a simple as placing it inside a plastic bag, covering it with a condom, or enclosing the alarm in a waterproof container. Run the tripwire connector out of the container at a slight downward angle to ensure water doesn’t run down the line and into the container, and paint the container to match whatever surface it’s attached to. Ensure that you have some method of easily attaching the alarm container to a tree or post – I bolt on vertical strips of thick plastic with holes drilled in them to the back of my alarm boxes so I can easily attach them using nails, screws, wire or zip ties.
If you’re using a local alarm like the personal noise alarm or a flashing light you may also want to consider installing it up high and out of the reach of anyone that trips it – that way they can’t quickly smash it, giving you more time to localize where the alarm is coming from. Use screw eyes to route the tripwire where you need it.
You can also trigger multiple signal types and combinations of local/remote alarms with a single tripwire. For example, you could tie the alarm end of the tripwire in a ‘Y’ and connect one tail to a clothespin that activates a remote transmitter and the other to an aerial flare that fires when it trips. This can be useful for creating alarms that will alert you in a wide variety of lighting and weather conditions – a flashing light might not be noticed during the day and a siren may be difficult to localize at night, but when combined the two provide a much better solution.
Tripwires also don’t have to be physical wires – you can also use lasers or infrared light to set up a tripwire. This typically requires a device or reflector at each end of the virtual ‘wire’, and some of them can cover a very long distance. I use an active infrared sensor part of my system to cover a row of windows in the front of my house (from the inside). Even though some of these devices are rated for outdoor use I’d recommend caution when doing so – heavy rain or snow, falling leaves, etc. can generate false alarms.
Continue reading“Elements of a Security System – Part 4, by J.M.”