Regarding the recent articles on perimeter security, I’d like to add my two bits. Get a solar powered motion detector light from Harbor Freight,
Instead of driving the light, have the unit power an HF frequency clock chip like this.
When the security light detects motion, it will power the RF transmitter, sending signals to your HF receiver. All that is needed is the chip, 5.1 volt zener diode with load resistor or 5 v regulator like 7805 or two diodes in series to drop the 6V to 5V just, and an antenna. – MH in Texas