Radiation is a harmful process which cannot be sensed by human. Normally you don’t need to measure radiation level but if you think there is a risk then it is worth checking. Changpuak have designed a homebrew Geiger – Müller counter using a counter tube from Distrlec.
In order to use such tubes there is a high voltage needed (~500V). So he split his design in to two parts that evolved in to two separate PCBs. First one is dedicated to generating high voltage using standard chopper circuit using 555 timer chip. It rises voltage from 9V up to 400-900V. Second PCB holds Geiger tube, Atmega16 microcontroller and MX232 for USART communications. Also value is displayed on standard LCD screen. This counter is able to detect β and γ radiations that are deadly to human.