When the man who annoys squirrels came around in his jet-black Ford, he grabbed a ladder and what appeared to be disco lights, and fixed his pale eyes on the dormers and rafters above him.

The party in an attic on Church Street would soon be over.

"These squirrels had access to everything here. Anything they wanted, anytime," Bill Earl, 68, said by the sidewalk of the three-story home in West Chester. "When you have squirrels living in a house for so long, they own the house. They own it."

Earl, of Norristown, spent his early years as a machinist in research and development, and also repaired roofs and gutters. Up on his ladder, he came face to face with all sorts of critters.

"There were squirrels screaming at me all the time," he said.

Earl began to ponder squirrels, and put his R&D cap back on, searching for some way his customers could get rid of them for good.

"I was at a stop sign and I thought: 'Touch, taste, sound, smell. How about sight? How about something that annoys their eyes?' Then it just popped in my head."

The illumination that came to Earl that day more than a decade ago was the Evictor, a high-intensity strobe that flashes twice a second, the right rate to annoy a squirrel and make it leave. He now has a patent on the application and makes the units at his company, Pest Tools, in Norristown.

"It's a strobe light you have to leave on all the time, like a disco that never stops," Earl's son, Ryan, explained.

Julie Cottage thought it was "cute" at first when she realized her West Chester home came with squirrels. She first grew disillusioned after reading about the fire hazard they posed. She tried plastic owls and a trapper who used fox urine, but the squirrels remained defiant and soon returned.

"We did everything aside from poisoning," Cottage said.

Cottage said the rodents peered at the family from a drop ceiling in the bathroom. They dropped nuts down the walls, even onto her dog Bridget's head. It was as if they were taunting her family.

"My kids started thinking the house was haunted," Cottage said.

Cottage's home was a real challenge, Earl said. He scanned the trees around the home and noticed they were devoid of squirrels. Her attic was the party house of the neighborhood, and once he booted them, he had to seal off all the entryways they'd created.

"They're so diligent," he said. "If they have an opposition to something, that's almost like a challenge to them, and they want to go back and chew their way back in somehow."

Squirrels, Earl added, are unpredictable, too.

"They can be really scary," he said. "I tell people, 'If you're going to put the light in, bang stuff around.' If I see a squirrel, I throw something at them."

Earl sells the Evictor worldwide and it's big in Florida, Texas, and California, where it's used to fluster roof rats. The strobes work well for skunks, too, he said, but not bats. Earl said the strobe isn't fast enough to cause seizures, but he does find dead mice in the attics from time to time. It also works on humans, his son noted.

"It makes you nauseous," Ryan said. "I just poked my head in there and had it on in my face, and I started to get motion sickness."

Earl says some in the pest control industry haven't fully embraced strobes. Trapping squirrels, he said, is only a short-term fix because their scent stays behind and draws more in.  That, he noted, just gives trappers more business.

"The trappers won't give me the time of day," he groused.

Asked whether strobes were effective, some members of the National Wildlife Control Operators Association responded with mixed opinions. Some said the strobes were expensive.

Earl charges $130 for each unit. The bulbs last 7,000 hours.

One pest professional from the New Orleans area said the product provides "a poltergeist effect on a home."

Cottage doesn't mind haunting the squirrels, though.

"We all sleep at night," she said.