San Francisco police officers helped Apple Inc. investigators look for a missing iPhone prototype that was left in a city restaurant in July, the police chief said.

That's the he second time in two years Apple has lost an unreleased smartphone.

Apple employees called San Francisco police directly, wanting assistance in tracking down "a lost item," the police said. Apple had tracked the lost item to a house located in the 500 block of Anderson Street in San Francisco. Four police officers accompanied Apple employees to the Anderson street home. The two Apple employees met with the resident and then went into the house to look for the lost item. The Apple employees did not find the lost item and left the house.

There was no record of the officers' involvement in the search because Apple did not want a lost property report created, the police added.

Apple officials have declined to comment on the case.

The Cupertino, Calif.-based company is reportedly planning to release a new version of its popular iPhone this fall.