Flick the switch on these flashlights and they don't light up. They blow up.
Three such bombs have exploded within the last month in the Phoenix area, causing minor injuries to five people and raising fears of more serious ones.
Police still have no idea who is behind the attacks and have put up 22 billboards across the metro area to warn residents about discarded flashlights.
"The nature of the bombings are so random," said Tom Mangan, a special agent at the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives in Phoenix.
Mangan said the agency has ruled out any connection to terrorism because the targets have been random and there have been no messages or demands.
The ATF said the bombs appear to have been made by the same person or persons because their design was identical.
An explosive was placed inside the flashlights with a smaller battery and rigged so that turning them on would send an electrical current that triggered the blast, Mangan said. He declined to identify the explosive material.
The first bomb was spotted by a passer-by on May 13 in a suburb just west of Phoenix. It was behind a palm tree in a strip mall and blew up when it was clicked on.
The next day, about 10 miles away, a landscaper found a flashlight in an irrigation ditch. It, too, exploded when he flicked the switch, authorities said.
The third bomb exploded on May 24 at a Salvation Army distribution center near downtown Phoenix, about 11 miles from the first one.
An employee detonated the device while sorting through donations, forcing 120 people in the store to evacuate.
The Salvation Army stopped accepting donations of flashlights. Since the explosion, employees have not seen any flashlights matching the yellow one seen on the billboards.
In addition to the billboards, police are offering a $10,000 reward for tips that lead to an arrest or conviction.
Police have received dozens of calls reporting possible flashlight bombs that turned out to be either false alarms or hoaxes, including one from a Goodwill store.
The bombings have stopped, though it is unclear whether there are more flashlights out there.
The attention may have scared the bombers off or they may gain confidence and strike again as the investigation stretches on without an arrest, criminal profiler Gregg McCrary said.
Mangan said the remnants of the bombs are at a laboratory and being studied for fingerprints and other DNA evidence. The ATF said it will try to trace the materials used in the bombs to see where they were bought.