HC-SR505 Mini Infrared PIR Motion Sensor, Micro IR Pyroelectric Human Movement Detector Sensors Module (Pack of 5)

They're good. I'm using em for Arduino projects

This is compact size PIR motion sensor. The price seems to be good for a batch of 5.

Do NOT purchase these sensors. They do not work due to very poor manufacturing quality. The first one I opened from packaging had wires not soldered to the board correctly. Thus it failed to work. And so it continued. Since I have no way to contact the seller, I can't request any replacement for faulting components. In the photo above, one sensor has wires NOT soldered at all. And another sensor, the wire is soldered but it is in the incorrect position such that it fails to work. Did anyone do any quality control? Apparently NOT.

Great for the intended use. Not super accurate, but if you purchase these you are most likely not going for a highly accurate motion sensor. I use these for DIY animatronics and they work great for that purpose.

Datasheet: "The file you are looking for is no longer publicly accessible."

These turn on when in a room with nobody in it. I bought them for an alert system, so they are useless to me.

One sensor was not working, but I tracked it down to a bad solder joint on the sensor module. ( I have a different issue now, but I believe it to be my wiring, so I will not report it here.)

They did not work!

I tested all 5 that came in the package. All worked, so at least they meet that level of quality. That said, quality on the soldering could be better, as even the vendor points out in one of the product pictures where it says you may need to add a little solder. Mine had varying levels of solder, some were pretty marginal but others were better. They are losing a star for this - they are getting their customers to do their QC and rework for them. As far as actual function goes, they are quite sensitive. When testing, some in particular would sense the slightest twitch at a couple feet range. I tested up to 6 feet and they were sensitive out to that range. Presumably they work past that, I just had limited space where I was testing. The non-adjustability may cause some design challenges, depending on how you want to use these. Based on my timing, they stay on for about 8 seconds once triggered, and will stay on longer if motion persists during that time. With the high level of sensitivity, I suppose you could adjust that by applying additional filtering - another layer of frosted plastic or something would decrease sensitivity, but it would be nice if there was a way to adjust this electronically rather than mechanically (many of the units out there include a trim pot). For the right application these will work well. Otherwise you may wish to choose another alternative that allows a little more adjustability.

These PIR sensors are a very convenient size and offer good sensitivity (a hand alone is enough to trigger them) and noise rejection. Direct outdoor light does not seem to effect operation. The output latches-on for about 8 seconds after detection, so that needs to be considered for some uses.