I am going to work on a project, which requires reliable movement detection.
It needs to work for approx. 1 year, with multiple movement detectors a day.
No problem. Just put it within range of an electrical outlet.
The sensors will be placed at 3 different locations at a spiral staircase, and should be activated when people are present in it's area.
And will the sensor know that there is someone near, if it is not active? I think you have that concept backwards. The sensor is always active, monitoring for motion/heat/whatever. It outputs a different value if there is something present than when there is not.