Mystery Frequency Disrupted Car Fobs in an Ohio City, and Now Residents Know Why
The answer (excerpted from the linked article):  The source of the problem was a homemade battery-operated   
  device designed by a local resident to alert him if someone 
  was upstairs when he was working in his basement. It did so 
  by turning off a light.

  “He has a fascination with electronics,” Mr. Glassburn said, 
  adding that the resident has special needs and would not be 
  identified to protect his privacy.

  The inventor and other residents of his home had no idea 
  that the device was wreaking havoc on the neighborhood, he 
  said, until Mr. Glassburn and a volunteer with expertise in 
  radio frequencies knocked on the door.

  “The way he designed it, it was persistently putting out a 
  315 megahertz signal,” Mr. Glassburn said. That is the 
  frequency many car fobs and garage door openers rely on.

  “There was no malicious intent of the device,” he said in a 
  statement.

  The battery on the device was removed and the signal 
  stopped. “It was a relief,” Mr. Glassburn said.