I reside in southern California in a semi-rural area; however, I do live in a housing tract. When SHTF, my concern would be the security surrounding the perimeter of my property. I do live on a corner property, thus, two sides of my property are of concern. I have come up with a plan for security notification when anyone enters my property or even gets close.
I found an inexpensive item at Harbor Freight  that will accomplish this notification. The item is an infrared triggered Wireless Security Alert System (Item Number: 93068). The battery operated unit has a range of 400’ from sensor to receiver. The retail price is $13.99; however, there is a savings coupon on Harbor Freight’s site good until 1-2-17 for a unit price of $9.99.
The units are customer rated at 3.8 out of 5.0 with a total of 773 reviews. As long as there are no bushes or tree limbs in the immediate area in front of the sensor, there should not be problem.
I have purchased three units to be installed once it is apparent that there be will a need to secure the perimeter of the property. Installation should be easy and fast, as everything is battery operated. I also have purchased extra batteries for each unit. Check the channels used by each unit that are stated on the box. It is important to purchase units with separate channels to avoid a conflict between multiple units.
I hope this suggestion can help others. – KL