It is hard to think that a flashlight or cellphone would have a power supply strong enough to do that much damage. (Although actually, metal halide lamps can sometimes cause UV radiation burns if they are damaged... http://archpedi.ama-assn.org/cgi/content/full/158/4/372 ).

As long as the backscatter machine doesn't run on Double A's, my fears are actually more reasonable than yours.

The backscatter machine presumably uses some sort of electrical plug to connect to power. It isn't inconceivable that it could receive more power than intended and produce more x-rays, or that something could go wrong with the shielding allowing x-rays to leak, or that something could go wrong with the x-ray bulb and we could produce the wrong type of radiation.

And it doesn't have to be 'burning your head off' to be a problem, it could simple produce an order of magnitude or two more radiation than intended, and be a health risk.