THE beacons are here. And they might not be all bad.

Beacons, tiny low-powered radio transmitters that send signals to phones just feet away, have quickly become a new front in the advertising industry’s chase to find you whenever, and exactly wherever, you are.

Although most consumers are just learning about these devices, tens or even hundreds of thousands of them have been installed across the country: outdoors on buildings, inside stores and even at National Football League and Major League Baseball stadiums.

The point of the devices is to send a specific signal, using low-energy Bluetooth, to phones that come into proximity, as long as those phones are running apps that can respond to the beacon. Those codes then set off an action on the phone, like a coupon, a reminder, a reward or just information. A beacon at the gates of a baseball stadium could open a map to the user’s seat and offer a beer or hot dog coupon.

Already, though, pitfalls have emerged. Last week, BuzzFeed reported that an advertising company had installed hundreds of beacons in phone booths across New York, with the city’s permission. The devices could communicate with a select few apps on people’s smartphones as they passed by, pushing advertising to those phones. Shortly after the beacons’ presence was reported, the city ordered that they be removed.