A US company has unveiled a wearable Java computer that can open doors and be used as a trusted electronic signature.

The iButton from Dallas Semiconductor is a 16mm Java-based chip embedded in a stainless steel can. It can be used as a physical key to enter buildings or as a computer key for secure network log-in, as well as for trusted electronic signatures.

The device features 64Kb Rom and 134Kb Ram, and can store more than 30 digital certificates. It also includes a Java Virtual Machine to launch Java applets.

Dallas Semiconductor plans to target companies interested in using Java-based hardware tokens that have higher levels of security beyond user names and passwords for network access, door access control, and secure email transmissions.

The company said it chose Java because of the technology's so-called write once, run anywhere platform, and added that the device is capable of running multiple applets because of its large memory capacity.

Applets can include profiles used to fill out internet forms, digital signatures for ecommerce, and digital photos and fingerprints. The iButton can also be updated for web-based applications.

The chip can be built into rings, watches, wallets, badge holders and metal cards. To gain access to buildings or PCs, users press the iButton on to a device called a Blue Dot that transfers information to and from the wearable computer. Blue Dot Locks are made by door hardware companies and follow standards that allow any iButton to operate with any Blue Dot Lock.

Michael Bolan, vice-president of product development at Dallas Semiconductor, said the latest accessory, the so-called 2-in-1 Fob, can be used for both physical and computer access control.

"One end of the Fob holds an iButton for door entry and the other end has a protected universal serial bus connector for universal access to computers," he said. "The iButton is a super-capacity smartcard with the reader built-in."

Customers include distribution company Ryder, which has kitted out its truck fleet with iButtons to track vehicle maintenance, and the city of Istanbul, Turkey, whose citizens use the technology to store digital cash for use on the country's mass transit system.