A New Jersey hospital and an insurance company have agreed to implant volunteer patients with Radio frequency ID tags, but one skeptic said implants are not quite catching on among the general public.

VeriChip Corporation announced Monday that it is working with a hospital and an insurance provider to implant some chronically ill patients with RFID chips. Hackensack University Medical Center and Horizon Blue Cross Blue Shield of New Jersey are asking patients to volunteer for a two-year program that will test "personal health record modules" inserted just beneath their skin.

The devices are about the size of a grain of rice and emit radio signals with individual identification numbers. The U.S. Food and Drug Administration approved them for medical use. VeriChip also touts the potential for using the chips for identity verification at airport security checkpoints. Implants are used for limiting access to secure areas with confidential information and to track livestock.

The U.S. Department of Homeland Security has studied their potential for tracking people. A New Jersey police officer recently volunteered to be "tagged" or "chipped," and authorities have suggested using RFID for verifying identities of immigrants.

A few geeks are also paving the way with their own personal projects.

VeriChip's medical implants contain 16-digit numbers that will link to patients' medical histories and family contact information stored in databases. VeriChip claims that its technology could mean the difference between life and death in cases where medical emergencies leave patients unresponsive.

However, critic Katherine Albrecht, director of Consumers Against Supermarket Privacy Invasion and Numbering, said the readers and the tags are vulnerable to disruption. She said that if the Internet fails, doctors could be blocked from information in the databases and that areas with high volumes of radio emissions " like ambulances " could prevent readers from working.

Albrecht points to VeriChip's own statements and waivers as evidence of weakness. She also notes FDA warnings that patients with the implants should not have MRIs, since the metal devices could be pulled through the body.

She added that even though many hospitals have agreed to use the technology, she still found strong public opposition in a recent survey on the topic.

"Many hospitals offer the implant," she said. "That doesn't mean people are doing it. They may have the buy-in at the corporate level, but they do not have the buy-in from the patients. Maybe the next generation will be different, but people who are adults now are really opposed to this."