Hiding cellphones in your lap may not be enough to let you off undetected as police consider a report on the use of electronic cellphone detectors.

Electronic cellphone detectors could be used to nab drivers using phones. Photo: file.

A NZ Transport Agency survey found 43 per cent of mobile use by drivers was going undetected, and more assistance than just the naked eye was needed.

If motorists are caught using a cellphone while driving, they face an $80 fine and 20 demerit points.

Drivers are allowed to use hands-free mobile phones, but they must be completely voice-activated unless they are securely mounted, in which case the driver can operate them infrequently and briefly.

Police responded to 163 fatal or injury crashes attributed to a driver using a cellphone between 2011 and 2013.

Mother-of-two Tracey O'Brien was killed when the car she was driving crossed the centreline and crash with an oncoming vehicle on State Highway 2, at Loop Road, in Te Puna, on May 3, 2014.

Police say the use of a mobile phone and lack of seatbelt are contributing factors to the fatal crash.

Stuff reports, police say it will take time to consider the NZ Transport Agency's findings following research conducted by Opus.

Trials of mobile detectors have already been conducted in Levin, Porirua and Wellington after a self-report survey found 69 per cent of drivers admitted using a mobile phone while driving.

The trials were conducted along visual observations and the roadside observations recorded less than 10 per cent.

Researchers say the combined use of detectors and observation was most effective, since visual observation did not catch all users.

Detectors required more testing because it was possible they could register activity when drivers' phones sent and received data, downloaded emails, or received calls or texts with "no interaction from the driver".

The directional device, which detects phone frequencies, can show different levels of use.

They are used in prisons to find contraband cell phones.