[cmatteri]

You can buy (or build from a kit if you can solder) a functional geiger counter that will detect gamma radiation (what cobalt-60 emits) for under 100 USD. They're a bit too big to put on a keychain, but you can easily keep one in a backpack.

[dheera]

Or maybe they should outfit police cars and FedEx trucks with them? They could issue warnings if they drive by a radiation source.

[bigiain]

You might find https://safecast.org/ interesting.