Lalbazar: Mobile phones left behind in app cabs by forgetful passengersconstitute a fifth of the 2,000-odd handsets reported missing or stolen every month and are seldom recovered without police intervention.

Uber India had released data in March that showed Calcutta as being the least forgetful among five cities - the top four are Bangalore, Delhi, Mumbai and Hyderabad - where passengers had been surveyed. What the study did not say is how difficult it is to get back a mobile phone left behind in a cab.

The majority of drivers either refuse to accept that a passenger left behind a phone or blame the next person who sat in the car for the item not being found.

"What they usually do is take out the SIM immediately and insert a new one. We are still able to trace the phone even if just one call is made before switching it off for later use," a police officer said.

A few days ago, the police were able to trace a phone that a passenger had left behind in an app cab in Behala because the driver used the handset a couple of times immediately after changing the SIM. Tracking was made possible by the IMEI number, a unique identity assigned to each phone.

When the driver was interrogated by the police, he admitted to changing the SIM and giving the phone to his wife.

App-cab drivers aren't the only ones tempted to make a gift of someone else's loss. For every heartwarming story of a lost wallet, bag, phone or any other valuable being returned to its owner, there are many more instances of items never being recovered.

"In at least one instance, we traced a phone that had been left behind in an app cab to a passenger who had shared a ride with the complainant after watching a film in a multiplex on Elgin Road," the officer said. "When we asked him why he kept the phone, he said, ' Galti ho gaya (It was a mistake)'."

Lalbazar recovers around 800 lost phones each month.