![]() The PIR activates the first LED, and the microwave the second LED. ![]() These contain a PIR, which only when triggered (to save energy) activates a second technology to detect motion (often microwave) for a few seconds. What you are probably looking at is a dual technology motion detector, not a PIR. No other answers yet address #3 - the three LEDs. another cool method is a series of small mirrors to reflect an LED IR Laser beam for interruption but more costly.Then add in battery backup if your grid is unreliable. Just hack the sensor to an Optocoupler for an alarm signal. They are found in big box stores for outdoor lights and are very cheap to turn on floodlights. Then any small change relative to the AGC’s signal, triggers the light on. IR motion sensors are extremely accurate using pulsed IR to get an AGC average reflection back with a PD and signal conditioner. The idea is to differentiate changes in mV in the reflected “standing wave” off walls and anyone disturbing those paths changes the amplitude up or down so an AC full wave rectifier with a slow high pass filter and a comparator is all that’s needed. I found by accident this worked to 10 yds in a lab when tuning a dipole back in the 70’s and later found commercial solutions doing the same. This is the same as using RSSI on a Return Loss bridge. VHF or UHF signals in a quiet channel using a splitter on one of the 2 ports can measure reflected signals off walls and detect reflections up to 10 or more wavelengths by using a Schottky diode and amp to detect changes in level using a constant power amp of ~100mW or so. There are probably many more, and depending on you exact use case, some or many may or may not be applicable. vibration sensors (MEMS or piezoelectric). ![]()
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