Pieter Franken affixes the Safecast radiation monitoring unit on a Hong Kong taxi.Alexis Lai/CNN
Safecast devised a radiation monitoring unit, containing a Geiger counter and GPS, to be affixed on the window of a vehicle.Alexis Lai/CNN
A handheld device to track the Geiger counter's results while inside the car.Alexis Lai/CNN
A Hong Kong taxi kitted out with Safecast radiation monitoring gear.Alexis Lai/CNN
The 'pancake sensor' used inside the Geiger counter to measure radiation. Radiation rays collide with the atoms of the gas inside a tube, creating a pulse. The number of counts per minute can be converted into a hourly rate of microsieverts of radiation.