Android app that requires hardware attachment

[geeklinda]

As I posted here, http://chicagoandroid.com/forum/topics/apps-which-require-external?
I am looking for information on Android apps which require/use an
external device. I am having trouble googling for this because of the
unspecificity of the search terms "android hardware app require" etc.

Examples I have so far:

Oscium (app + hardware) which lets an iPad be used as an oscilloscope
http://oscium.com/
iPhone-attached geiger counter as in
http://www.tuaw.com/2011/04/15/iphone-geiger-counter-would-benefit-...
Square for Android (credit card reader) https://market.android.com/details?id=com.squareup