More seriously, it could be also very interesting to create a devices that produces it own electricity according to motion and embed it in something that makes it break if you open it (some kind of super resistant acrylic). Then, it would be super hard to hack it, which is the obvious first thing that everybody would like to do with such devices.

For exemple, i’m thinking about these little electro-delicacies,
the sugar-cube-sized electric generators that feed on environmental vibrations :
http://www.newscientisttech.com/article.ns?id=dn12190&feedId=tech_rss20

Cheers,
j*b