Here’s an amusing little device that Eric Taub writes about in the New York Times:

All of this is why a new product from Zomm may wind up hitting a nerve. A small electronic disc that fits on a key ring, the product, also called the Zomm, connects to a phone via Bluetooth. Separate the two devices by more than 30 feet, and the Zomm first vibrates, then flashes and then screams.

Mr Taub notes that one disadvantage of the device is that there’s no way to alter the 30-foot distance before the alarm goes off; depending on where you are, 30 feet could be too far. Indeed, it could be... but there’s a good reason the distance can’t be controlled. 30 feet is a familiar number: it happens to be the nominal range of Bluetooth. That means the device is just detecting when the Bluetooth connection with your phone fails, and it then screams about the failure.

And that means that it won’t know the difference between a connection failure that happens because you left your phone in the bar and walked out, and one that happens for another reason — perhaps your phone’s battery is low and the Bluetooth shuts off automatically, or perhaps you turn the Bluetooth off yourself, forgetting the Zomm device’s dependency on it.

What’s more, the Bluetooth range can be drastically less than 30 feet if there are interfering factors, such as walls, machinery, and even people blocking the way. It can also drop because of radio-frequency interference. Lend your phone to a friend at a party and walk across the room to get another drink... and even if you’re only ten or fifteen feet away, you may find yourself loudly embarrassed (unless, perhaps, you can use it as an opportunity to brag about your slick toy).

It is a clever idea, but, as Mr Taub points out, it’s expensive and impractical. Still, I do have to give it points for the cleverness.