The night I realized my 'hidden camera detector' was just a magnet

Last Tuesday I got deep into a paranoid streak after watching too many airport surveillance videos on YouTube. I bought this 30 dollar device off Amazon that supposedly finds hidden cameras by sweeping for magnetic fields. For two weeks I was walking around my rental in Phoenix, waving it over outlets, smoke detectors, even my landlord's plant. Then my buddy came over, laughed, and put a fridge magnet next to it. The thing went haywire, beeping like crazy. Turns out it was just a cheap compass with a buzzer, not some spy gear. I felt like a total fool, but also kind of relieved my house wasn't actually bugged. Has anyone else bought junk like that and had the 'aha' moment hit way too late?