Kerry Wong did a teardown of a cheap GM3120 field strength meter:
There are a lot of cheap electromagnetic radiation testers out there which boast some quite impressive claims. So I decided to pick up a popular one (GM3120) from eBay to see how well it works. And perhaps more importantly, I wanted to take a look inside to see how the E field and H field sensing is done.
Most professional field strength meters feature a dome-like sensor. Housed inside are three orthogonally arranged antennas used for picking up field component in that axis. A cheap tester like the GM3120 clearly doesn’t utilize this kind of sensor topology and presumably can only discern field strength along a single axis.
See the full post on his blog here.
Check out the video after the break.