Create a sheet of material like bubble wrap that contains thousands of small gas pockets. Find a gas that responds to microwaves by changing color. Drap the sheet over a microwave and set it to run on high for a couple of minutes. Find the colored cells in the sheet to determine if you have a safe microwave oven.
Use the same cloth to show the microwave impact of cell phone use.
Here is a similar technology used to confirm even cooking IN the microwave.
<snip>We have developed indicators which would change color (e.g., red-to-green) when food has reached a predetermined temperature and humidity/steam. The microwave doneness indicators are steam/humidity & time-temperature indicators. They change color with time, temperature and humidity/steam. They don’t change color with only time, only temperature or only humidity. Our indicators change color, e.g., red-to-green/blue when the steam/moisture is produced for a certain period of time. These indicators are in form of labels. </snip src=”http://www.jplabs.com/html/__microwave_doneness_indicator.html”>