Listening to music with earphones that block the sounds of hazards is dangerous for anyone, particularly runners and cyclists.
A device called Fuser from Olens Technology remedies that problem by adding a microphone that pipes environmental sounds to headphones.
Fuser looks like an oversized iPod Shuffle, without the dial on the front. It is about 1.75 inches by 1.5 inches and about one-quarter-inch thick.
It is a microphone with a small amplifier and a volume control that allow you to decide how much outside sound you want to mix in. It can be turned from undetectable to loud enough to generate feedback.
The idea dates from the Sony Walkman TPS-L2 cassette player. One of the first personal, portable music devices that was not a transistor radio, it had two headphone jacks and a hot line button that activated a microphone so you could speak to the person you were sharing the music with and be heard through the headphones.
But there is a difference: The Fuser's microphone is always on, so if the case bumps you or rubs against something, you hear a loud thump through the headphones. If you run with it clipped to your sleeve, you will be treated to a rhythmic thump-thump-thump unless you fasten the Fuser securely to your arm.
The Fuser has a rechargeable battery with a claimed life of about 10 hours, and it will work with any device that uses a standard 3.5mm stereo headphone jack. Available through the Olens Technology Web site, it costs $30. ROY FURCHGOTT
This article originally appeared in The New York Times.