Since this thread is active... a couple comments.
1) the original plunger model was nearly impossible to get out without damaging when it came time to replace the battery. I destroyed two (and the batteries didn't last long or came low). I talked to the company and they actually sent me a replacement - the design has changed from the pics at the beginning of this thread and now there are provisions to screw it in (instead of just press in) and there's a spacer included.
2) I have a ton of the window version in my vinyl windows - those have all worked flawlessly; however I haven't been all that thrilled with the plunger ones. On my front door I had problems but they were rectified with a new battery; I also have them on my kids' rooms (so I know if they get up after bed time, and also to turn on the lights for them outside their rooms and in the bathroom) - but those two have given me problems not always working. I also have one on a hall closet to automate the lights - performance is ok like 95% of the time, but with security, you really want 100%. Also to note - because they're installed hinge-side, the door has to be open a little more to trigger these. May not seem like a big deal, but I want to know if my exterior doors aren't closed all the way.