Motion alrams mounted to the backs of hung pictures?

[Rick]

Anyone familiar with these? Years ago, I recall using these in a museum setting; we had some on-hand for occasional use (e.g. when a little picture was installed "around a corner", beyond direct-line-of-sight or was otherwise vulnerable--they were kind of an intermediate step between nothing at all and using a security hardware system.

Anybody know know of a source for these?

[T. Ashley McGrew]

I know this may not be specifically what you are asking about. I remember seeing products that have been around for a while that may be closer to what you have in mind. Another solution though that not only addresses concerns that you are describing but also a whole host of other needs involve the use of an active RFID system. These aren't just the labels that go beep when you walk out of a Best Buy or whatever if the clerk doesn't clear your purchase (passive systems).
The kind of unit that I have worked with is about the size of four credit cards stacked on top of each other. They can be placed on the back of 2D items on the wall or used as wireless alarms for cases or whatever. They can be set to react to different kinds of input and to different levels of vibration and can be connected to your main security system which can set off audio alarms or just provide specific information about the individual object effected and what location it can be found in etc...
This is probably beyond what you are thinking about on the short term but worth considering on your wish list for the future. Here is a site that has different versions of this kind of product.
http://www.isisasset.com/products/prd_arts_galleries.htm (http://www.isisasset.com/products/prd_arts_galleries.htm)