Police called in for search as 'priceless' prototype iPhone 5 is left in Mexican restaurant in San Francisco, according to report

Have you heard this one before? An Apple employee walks into a bar in California with a top-secret iPhone prototype – and leaves it behind. Apple then scrambles to recover the phone, involving the police in the process after it has been sold by a finder, eventually getting it back under wraps.

It happened in April last year – and now, says CNet, it has happened again with a prototype of the very latest iPhone, expected to be launched within the next few weeks.

But this time Apple does not appear to have got the phone back.

According to the report, the phone was lost while being tested outside the Apple campus in a Mexican restaurant in San Francisco's Mission district, and then sold on Craigslist for $200 (£123).

It was initially left in a bar called Cava22, which says it takes "real pride in bringing a live and festive Mexican experience, for all our cleints [sic] to enjoy" including a margarita sweet-and-sour mix, by an Apple employee who appears to have been testing it off Apple's campus. The company carries out external testing by letting selected staff take prototypes to urban and other locations in order to test its behaviour in normal settings, rather than the laboratory conditions of its own headquarters.

But they are not meant to leave them behind. "I guess I'll have to make my drinks a little less strong," the owner, Jose Valle, told CNet.

CNet says Apple contacted the San Francisco police as soon as the loss was discovered and told them that the phone was "priceless" and that the company wanted its safe return.

It was eventually tracked down via a location-tracking system built into the phone to a single-family home in San Francisco's Bernal Heights area, says CNet. But when police and Apple's investigators visited the house, the occupant denied any knowledge of the phone, and it wasn't recovered despite a search – with the occupant's permission – of the residence.

Apple has not commented on the events, which come as interest in the successor to the iPhone 4 – which has variously been guessed at as being called the iPhone 4G, 4S and iPhone 5 – is growing. With the existing model now comparatively old in smartphone terms, having been released in June 2010, the expectation is the next model will have to bring dramatic improvements in performance to compete with rival handsets from companies such as Samsung, Motorola and HTC using Google's Android operating system.

New versions of the iPhone are expected to use more powerful processors and have a different arrangement of the antenna system in the casing. The external antenna caused a media furore last year after some users complained that reception seemed to drop when their hand completed a contact between two metal components. One source at a carrier company suggested to the Guardian the problem arose because the prototype phones are principally tested on the Apple campus, in areas with relatively strong mobile signals; the signal drop from the antenna "bridging" was principally seen in areas with weaker reception.

Apple is understood to provide carrier companies with iPhones for testing that are shipped in sealed boxes so that staff cannot see the exterior. The tests are necessary to ensure that the phones comply with network software requirements.

Last year a prototype of the iPhone 4 was left in a beer garden by Gray Powell, an Apple engineer. That eventually made its way to the gadget blog Gizmodo, which published pictures and a video of the device. Apple called in the police, who got a warrant to search the home of Jason Chen, Gizmodo's editor. Early in August, prosecutors in San Mateo filed criminal charges against two men, alleging that they sold the iPhone 4 prototype to Gizmodo. It is illegal under California law to take lost property if you know who the owner is likely to be, punishable by up to a year in prison.