When the Frankfurt International auto show opens its doors to the public on September 14, leading automotive equipment and tech provider Bosch will be demonstrating a new digital feature called Perfectly Keyless, that can turn any driver's smartphone into a hands-free car key for opening and closing doors.

"Perfectly Keyless, our digital vehicle access system, means that drivers will be able to do without traditional car keys. It's a great example of stress-free connected mobility," explained Harald Kröger, president of the Bosch Automotive Electronics division.

The system is simple and secure, requiring a sensor fitted to the car that can wirelessly connect to an individual phone for identification. The user doesn't even need to take the phone out of his or her pocket. "Once this identification has happened, the vehicle is unlocked without any need for a physical key. Similarly, no key is needed to start the engine or to lock the car again at the end of a journey," said Kröger.

In recent years, carmakers have been embracing the possibilities of the smartphone, whether as a tool for programming a vehicle's navigation system, or for remotely checking its location, its fuel reserves or, in the case of electric cars, the amount of charge remaining in the battery packs. In the case of Mercedes, BMW and Audi, your handset can even be used to remotely park or summon the car.

However, as Bosch is an industry-wide global supplier, its system can be adopted by any car company in the world and all a driver will need to take advantage of it is to install the supporting app.

And, if a car has several drivers, when the smartphone connection is made, the car can also automatically adjust settings, such as seat and mirror positions and radio stations, in line with that driver's preferences.

The system is also future-facing. With the growing popularity of peer-to-peer car rental services, Perfectly Keyless can be used to enable other people to access a person's car (with their permission) without having to use car keys. What's more, the app allows drivers to set a time limit and geographical boundaries for another user's key -- something that could be just as effective for parents worried about their teenage children's driving habits.

And as innovative as Perfectly Keyless sounds, so far, the best alternative digital key system is Jaguar Land Rover's Activity Key. It's a slim waterproof wristband that doesn't require a battery and which will automatically lock and unlock a car. The idea behind the device is that many drivers, especially those of proper SUVs want to head out on adventures and leave their valuables securely locked in the car -- including the car keys and their smartphone. As long as they're wearing the band, the traditional key fob and any access apps on their phones are automatically disabled.

The 2017 Frankfurt auto show opens to the press on September 12 and to the public from September 14-24.