Notes on RCWL-0516

According to the datasheet the minimum operating voltage for the RCWL-0516 is 4 volts, however, in my tests they appear to operate perfectly fine at voltages as low as 3.0 volts (and possibly lower). While it's entirely possible that the detection distance is reduced as the voltage falls, it is not a major concern as during my test, I could not enter the room without triggering the device even when the supply was at 3.0 volts.

LiFePO4

I plan to use a LiFePO4 battery (fully charged to 3.6 volts) to power the circuit thereby eliminate problems associated with having to reduce higher supply voltages to power a 3.3 volt microcontroller or similar device.

Test Method

Power the test device with a fully charge LiFePO4 battery charged to 3.6 volts and ran tests every few minutes over the course of two weeks (the device was powered continuously 24/7).

When testing I simply  turned on the multimeter (I could see this from a distance) and left the room. I waited a few seconds for it to settle and reentered the room. Each and every time I tested, it triggered perfectly.  Note I also tested for potential false triggering in an empty room, but there were none...

Recorded the battery voltage at the end of each day to facilitate further analysis. Currently into week three but the battery has not yet dropped below 3.0 volts so finding are as yet incomplete...