I'm a big fan of my Front Point system, but I'm noticing that the "sticky pads" that can be used to attach the sensors to the walls don't last forever. I know it's probably more prudent to nail the sensor in, put it on a shelf, or something, but since these sticky pads are included, you'd figure they'd plan ahead as far as their usability and reliability is concerned.
How about changing those out with the poster type self-adhering things you can use to hang up giant wall posters? Those are super durable and should be able to handle a little motion sensor (and then my alarm system won't go off when a motion sensor comes crashing to the floor while I'm on vacation, lol!)