Similar technologies are being developed elsewhere. For example, the MagneTrace system, designed by engineers at the Georgia Institute of Technology, records when magnetized pills pass through a patient's esophagus and sends the information to a computer. The Raisin system takes the additional step of incorporating on- and in-body sensors that correlate pill taking with the body's physiological responses.

Privacy issues are an obvious concern with a technology such as Raisin. Savage says that because the pill's signal is transmitted electrically through skin tissues rather than by radio, it couldn't be picked up remotely by, say, a company wanting to know what medications its prospective employees are taking. Proteus adds that security safeguards would be used to protect transmitted data.

And because the signal doesn't go beyond the skin, the pills in one person's stomach wouldn't trigger the receiver in another person's body. Proteus says that even if two users came into physical contact, the conduction of electricity from one person's skin to the other's would be too weak for inadvertent data exchange to happen.

While acknowledging that privacy concerns need to be addressed, Savage offers an optimistic vision in which the technology enhances community support by enabling the sharing of information. As an example, he points out that people managing mental illness usually want to stick to their regimens, but the nature of the problem makes it difficult for them to do so. The Raisin system would alert relatives if the patient misses a dose.

The system would also eliminate the need for direct observed therapy, he suggests, in which patients with contagious illnesses such as tuberculosis are required to be observed by a health-care provider as they take each dose of their medication. The Raisin system would achieve the same goal with less intrusion.

"If clinical trials show that this complicated technology is safe and effective, it has the potential to be very useful in monitoring patients' adherence," says Olga Klibanov, an assistant professor at the Temple University School of Pharmacy, who works with inner-city HIV patients and was not involved in research on the Raisin. "Data that can be collected with this tool would likely be useful--not only in a trial setting, but also to clinicians in taking care of patients."

So far, Proteus has raised $60 million from investors including the Carlyle Group and Kaiser Permanente Ventures, and it has filed more than 250 patents. Clinical trials with human users began earlier this year, to test the functionality of the IEM and sensors. The company hopes to have the system on the market in 2011.