Motion sensor light switch modification

I'm looking to add a circuit with some Arduino additions including a to an installed wall motion sensor switch. Has anyone used a wall switch as the basis for a project before that they might be able to shed some light on how to attach to it? At the most basic level just having access to the power output from the switch being on or off is what's needed, though potentially accessing the timer later would be handy.

I'm having a bit of trouble finding a description of how to do this and don't have a switch I can disassemble before starting. Thanks!

It's not really safe to assume that all PIR wall switches are the same. You should probably take one apart or at least specify the model you intend to use.

Many (but not all) PIR sensors have an open collector output. This is ideal for interfacing to an arduino, just connect it in and enable the internal pull up resistors.
You can test this by measuring the output, if there appears to be no signal on the output when you measure the voltage then it is an open collector system. First of all just try connecting that output to 5v through a 10K resistor, if you can now measure an output that changes when someone is detected it is defiantly safe to connect directly to an arduino. You also have to connect the ground of the sensor to the ground of the arduino.

Great, thanks for the help. I’ll see if I can find a PIR switch at a hardware store to take apart, then, and test it that way. Also, when you say to connect the output to 5v through a 10K resistor, is that hooking it up through a wall wart / DC power supply?

Yes power it in the normal way, then do your test.