I read a magazine in 1967 that said you could build a UFO detector with a compass needle, some wire, some wood, and a plastic breadbox. It said that UFOs give off a strong magnetic field. Since I had a large collection of stereo tapes, I decided to build it, not only as a UFO detector, but as a detector of any events that could harm my music collection.
The device is essentially a compass needle with a copper ring placed around one of the poles, and a copper support for the pivot. If the needle deviates any from pointing north, it completes a circuit and rings a bell. I placed the detector on a high shelf, to be closer to UFOs and far enough from my tapes to warn me before damage could be done.
I operated that detector for many years, and didn't catch a single UFO in the act with it. Even during a major flap here in 1973, it did not sound. I don't mean it never sounded. It did go off a few times. Each time, I checked for someone in the room with a magnet first, then went out to see if a glowing blob of light or something else was visible. Then I tracked down the real cause of the alarm. Here are the real stimuli that set it off:
Not one alien! Not even a glowing amorphous blob! Just mundane activities. This made me realize that UFOs probably do not cause the "magnetic" effects observed by witnesses. A shaking witness (frightened by a fire balloon or some other unusual stimulus) can easily start a compass spinning. The effect seen on 7/3/65 in the Antarctic Sea has been shown to be a malfunction in a magnetometer.
Lastly, if UFOs have strong magnetic fields, where are all of the people complaining about erased stereo tapes, video tapes, and computer disks? I would think there would be an epidemic of this. Very few cases of erased tapes happen, and most have mundane causes (e.g. kids playing with little refrigerator magnets). A low flying magnetic UFO should cause hundreds of cases, concentrated in the area of the sighting. Only one case has appeared with any music tape damage, and those were 8-track tapes, which wear out quickly (Condon case 39, Lake Elsinore CA, 11/8/67).