Are you sure, DL?
I was only talking about the ICAO legal definition of how the black boxes must be designed for airliners. Only Underwater Locator Beacons are mentioned on the NTSB page about the black boxes and they are most definitely activated by water.
http://www.ntsb.gov/aviation/CVR_FDR.htm The logic behind this is that if it hasn't sunk, you won't need an ELT to find it.
You didn't say what you fly, and maybe you have a g-force activated one too, but I suspect that's a rarity.