"security" Cameras

so here's the deal: my mother works at some place and is pretty sure some dude is poisoning her food/drinks with antifreeze or something. (yellowish liquid, no discernable taste or smell)

What's a good camera to get that is cordless?
Also as small as possible, and not black/white.
We're going for cheap here, but it'd be good to have a selection, in case one is far better or something.

not monochrome I meant