I have a driveway that is over 300 feet long and it is nice to have some advance notice that someone is driving or walking in. Previously, I have used a very expensive IR beam-break detector. It gave a lot of false alarms and eventually failed due to a lightning strike. It also required that I run a very long cable that could survive outdoors, which added more expense. It’s time to switch to a wireless sensor.
I found this inexpensive one at Harbor Freight ($17 with coupon.) It is a simple, stand-alone alarm with a receiver that just flashes some LEDs and emits a tone. It claims to work up to 400 feet and I verified that it works to at least 350 feet, which is good enough for my application. I created the circuit described below to interface this to my Raspberry Pi based home alarm system.
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