Asked what would happen if a driver switched off his phone, a Meru official replied: 'Well, the driver can also disable the mobile data terminal, they will take just a minute to cut off the wire. There is no foolproof measure.'

Some radio cab services, including those operating in Calcutta, install dedicated GPS devices partly to minimise this possibility. Such devices are available for Rs 7,000 and upwards.

Even if they aren't foolproof, such devices can be made tamper-proof, according to a Mumbai-based firm that provides GPS solutions to media houses, finance companies, logistics companies and transporters.

'GPS devices can be installed out of sight of drivers and made tamper-proof,' said Ankit Zatakia, COO, Elixia Tech Solutions.

Where GPS can help is by allowing a friend or a family member to track a car. Uber allows users to share the details of a trip with others so that they can track the car. A family member or a friend can thus track a cab ferrying a woman at night even if real-time tracking by the company itself is not a promised feature.

Additional reporting by Zeeshan Jawed