The Looxcie ($199), a small wearable camcorder introduced recently, loops over the ear. The camera is built into a Bluetooth headset that streams digital images wirelessly to Android phones that use a free Looxcie app. From there, the clips can go directly to e-mail, said Romulus Pereira, chief executive of Looxcie, which is based in Sunnyvale, Calif. Soon the company will offer apps that make the camera compatible with other smartphones, he said.

The Looxcie is not a high-definition camera. It records at a resolution of 480 x 320 pixels at 15 frames a second. But it has a special button that makes it ideal for taking video of unexpected moments, Mr. Pereira said. When the camera is running in continuous-capture mode, and the wearer suddenly sees a goal scored at a hockey game, for instance, a quick push of the button will tell the camera to automatically save a clip of the preceding 30 seconds. Then the footage of the puck sailing into the net can be preserved and automatically e-mailed to friends. The camera weighs about an ounce and stores up to five hours of video, he said.

Michael Duplay, the technology director at the Stark County Park District in Ohio, recently tucked his Looxcie over his ear so it could record his first-person views of a walk in the woods. He also shot a video while he was driving, then sent the evidence of his car’s veering motion to his father for an expert analysis. (Dad diagnosed an alignment problem.)

As wearable cameras gain popularity, and as some amateur auteurs capture candid images of people with no wish to star on the Internet, the devices are sure to raise privacy and other issues, said Professor Zittrain of Harvard. “What will we do then?” he asked. “Ban them at basketball games and recitals?”

With proper procedures, though, the cameras could yield a trove of valuable evidence, helping future historians analyze what life was like in 2010. “We have painstakingly reconstructed ancient civilizations based on pottery and a few tablets,” he said. “I would love to leave this legacy instead.”