you could just keep your cell phone in your front shirt pocket, just cut a small hole in the pocket so the camera lens can see through. other than that you would probably have to get a "go pro" camera which are kind of expensive and more difficult to hide.
LOL
Wanna do this too and just watch it when i get home.
If only I had a shirt with a pocket.
The got some glasses with a hidden camera
In a couple years when they make these more discreet, you'll have your wish.