Called the Sentilla Energy Manager for Data Centers, the product uses small Java-based devices that plug into the back of each server and measure the actual and "reactive" power flowing to each machine. The devices aggregate the data over a wireless mesh network and send it to a Web-based administrative console to give a granular view of the power being used by each server.

The product can identify servers that are drawing power but not running any load, or be used to compare energy use among servers from different vendors or in different configurations, Davis said. It also works with storage gear and can help administrators to figure out the best time to replace their storage arrays, for example, which become gradually less energy efficient over time, he said.

Sentilla claims to have already signed one large customer for the product, a telecommunications carrier that it can't yet name publicly. It is also being endorsed by Sun Microsystems, which uses its product to demonstrate the energy efficiency of its servers, Davis said.

Sentilla charges for the product by the number of power measurement devices being used. They start at US$250 each but larger volumes cost less, and an order for 1,000 devices would be about $100,000, including the administrative software, Davis said.

The devices plug into a standard electrical cable between the power source and the piece of equipment, a bit like a mini-version of the power adapter used with a laptop. For server racks, instead of attaching the dongles loose to each machine, Sentilla makes a 1U component that slides into the rack and connects to the other servers.