Complete Home Protection

I tested the Microwave Radar Sensor 24/7 from a single 3.2 volt LiFePO4 battery for a period of 28 days and here are my conclusions...

The RCWL-0516 worked perfectly for 26 days at which point the battery voltage dropped to just below 3.0 volts and while the device continued to work below 3.0 volts it became more and more erratic as the voltage continued to drop...

• There was no measurable difference in detection be it a 4 volt supply or a 3 volt supply...
• Voltages below 3.0 volt (even if detection is possible) are not consistent and cannot be relied on...
• A single LIFePO4 battery will power the sensor reliably for 175 hours (25 days)...

In the real world I would recharge the battery every two weeks or better still, power the sensor from a near by main socket.

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...