It's true that radiation detectors are much more easily available to the general public than ever before. Apart from conventional Geiger counters there are solid-state alternatives that rely on photodiodes or CCD cameras. You could even get an app that transforms your smartphone into an improvised radiation detector. Not nearly as sensitive as a Geiger-Müller tube but sufficient for dangerous levels of Gamma radiation at least.

Also, it is easy to make your own Geiger counter if you have some basic electronics skills. I've played a lot with ex-Eastern Bloc Geiger tubes that are all over eBay. You can get one for $20 and they work very well. If anyone needs good schematics I'd be happy to help.

The only tricky part is the high-voltage power supply. This one is really good:
http://www.techlib.com/science/geiger.html

As far as power consumption (under 1mA if you know what you're doing) it is actually far superior to most commercial devices. A single 9V block battery or a couple of AA(A) cells will last a long time. The circuit can be calibrated to give a pretty accurate reading.