YOUR backbone's connected to your shoulder bone, your shoulder bone's connected to your neck bone - and your neck bone's connected to your cellphone.

Something along these lines is what Lin Zhong and Michael Liebschner at Rice University in Houston, Texas, envisage. They want to use the human skeleton to transmit commands reliably and securely to wearable gadgets and medical implants. Their research, funded by Microsoft and Texas Instruments, could also lead to new ways for people with disabilities to control devices such as computers and PDAs.

Wireless radio signals are already used to control gadgets and implants, but these can suffer interference from Wi-Fi and other sources. This makes them unreliable and, in the case of medical implants, potentially dangerous. They can also be hacked by anyone with an antenna, Liebschner points out.

So the Rice team decided to investigate using sound instead of radio waves. Bone is known to be a great conductor of sound, but so far it has only been used to transmit analogue signals in applications such as checking how bone is healing after a fracture, and in hearing aids that transmit sound from outside the skull to the auditory nerve.

To see if bone could transmit digital signals over longer distances - to a headset, say, from a sensor worn on the wrist - the team applied a small vibrator to various parts of the body. When they then measured the acoustic signals received elsewhere on the body, they found that a "frequency shift keyed" (FSK) signal gave the best distinction between 0s and 1s. In FSK signalling a 0 is represented by one frequency and a 1 by a different one.

They then measured how well bone conducted these signals when they were generated in places on the body where devices are normally worn: the wrist for watches, the lower back for cellphones worn on a belt, and behind the ear for headsets. They found the skeleton conducted even low-power vibrations from one location to another with surprisingly few errors. "This is quite amazing because all the links involved multiple bones and many joints," Zhong told a conference on body networks in Florence, Italy, this week.

The researchers suggest applications such as a vibrator in a wrist receiver/transmitter that could tell an implant placed near a bone to release a drug dose, with the implant then sending back data from its sensors. Similarly, tooth clacks or finger clicks could be interpreted by a receiver to activate, say, functions in a phone.

For Liebschner, the great benefit is security. "All data transfer is contained inside the human body, and it can only be retrieved through direct physical contact," he says. People could even swap information between devices via a firm handshake, Zhong suggests.