These days, the hardware of all smartphones is the same: gyroscope, accelerometer, GPS, etc. Yawn.
I have lots of electronic tools on my workbench that would easily fit into a cell phone. For example:
* Infrared temperature monitor. I have a hand-held model that is 99% battery and display.
* Ultrasound measuring tape. Hand-held model is all battery and display with a 30' range.
* LED to indicate where the first two are pointing. Also useful as a pointer when lecturing or showing someone where the CPU is in their PC.
What hardware do you think should be added to the next generation of smartphones?