Most cell phone users have done it at least once: scramble to silence a ringing phone hidden deep in a jacket pocket or bag. Casio has developed a prototype system that can mute a phone with a couple of taps to a wristwatch.

The prototype watch works with handsets armed with Bluetooth Low Power technology and a compatible app, and is slated to be commercialised at the end of the year. It's designed to alert a user to things like incoming email or calls to their cell phone.

If a phone is in a bag or pocket, the alerts would allow the watch wearer to find out who the call or message is from, without scrambling for the phone. Or, in the case of an incoming call, quiet the phone by tapping the watch twice.

Information flows both ways. With the push of a button, the watch can request the current time from the mobile phone and update itself. This could be especially useful when travelling, because cell phones generally take local time from the mobile network and automatically adjust to time zone changes.

The Casio prototype, which was demonstrated in Tokyo, can also help find a lost cell phone. Providing it's within the technology's range of several meters, the watch can make the phone sound an alarm so it's easier to find.

The system is based on Bluetooth Low Power, a new version of the wireless technology that uses much less power than current Bluetooth. Watches running the system stay connected to a phone 12 hours a day, and should be able to run for 2 years before needing a battery replacement.

Casio plans to open the communications standard to application makers to encourage its adoption in smartphones and other devices. It sees additional potential uses, such as using the watch display for information from a GPS device or sports heartbeat monitor.

A commercial watch featuring the technology should be available around the end of 2011 or in early 2012. That's about the same time as other Bluetooth Low Power devices should be hitting the market.

Casio's biggest challenge might be persuading people to put a watch back on their wrists. A recent UK poll found 1 in 7 people claim they no longer needed to wear a watch because they can get the time from a cell phone or other device.