Keyless automobile remote controls are rugged and run a long time between battery changes, but they can fail when in areas of strong electrogmagnetic fields.

EM field strength near a TV tower can interfere with remote keyless entry systems. Data courtesy of WHDH.

What does it take to interfere with a keyless entry system? To find out, I asked the transmitter engineers at WHDH for field-strength measurements. The figure shows measurements for channel 7 at 11 locations near the tower. The first nine locations occur in the shopping area.

I ran some experiments and found that at distances of roughly 1000 to 2000 ft from the tower, my remote control would either not work at all or would work only within a few inches of the car door. At locations 3000 ft and beyond, the remote would work at distances of 15 to 18 ft. The plot shows a significant drop in field strength at about 1300 ft, but my remote control wouldn't work at that distance even though the field-strength data indicated that it should. But this was an unscientific experiment and I was not at the exact locations at which the field-strength measurements were made. Furthermore, the field-strength measurements were conducted at the channel 7 and channel 42 frequencies only. Other channel frequencies could have interfered with the remote.

I didn't find an exact correlation between the field strength data and my experimental data, but I can still conclude that using a remote keyless entry system in areas of high EM fields will cause them to fail or to work only at reduced distances. Keep that in mind the next time you think a remote's battery has failed.