A computer program designed by an Auckland student had an unexpected spin-off this week when it led police directly to his stolen car.

Peter Hurt, 28, was at a friend's place in Mt Albert on Monday when his car was taken about 10.50pm.

But the car was fitted with a GPS device linked to a website - which showed in almost real time where the thief was taking it.

By visiting his website trailtrax.co.nz he could see the car had been moved 20 minutes earlier and taken for a joyride.

"I rang 111 and got on the phone to them and told them exactly where my car was. At the time it was in Mt Roskill."

The car had been to Westmere and Western Springs and cruised around several Grey Lynn streets.

Officers were sent to the scene but the thieves continued - and their exact movements were being watched by Mr Hurt.

By logging into his website he could get an update on where the car was every 40 seconds.

The third-year Unitec Bachelor of Computing Systems student was able to tell the operator the number and name of the street and the direction the car was travelling so the information could be passed to the pursuing patrol cars.

"I was on the phone to the police and they had seven police units and a dog unit out chasing them. It got to an address where they've actually ripped the GPS receiver off the dash so we lost it there."

Mr Hurt thinks the thieves would have heard the police sirens "all over the show and would have looked at the dash and realised and pulled it out ... Within four minutes of them pulling it off they've left the vehicle."

By the time it had been disconnected police had been following the car for about 15 minutes. When it was found in Shackleton Rd, Mt Roskill, the car was empty but with little damage aside from a smashed back window and ignition ripped out.

Mr Hurt told the Herald police phoned him about 45 minutes later and said he could come and get the car.

"The police operator asked, 'How are you able to do this, what sort of system have you got there?' and I said it was one that I've helped create."

He was stoked about how the system, called Trailtrax, worked, even if it was a purpose he never intended it for. It was designed with a family friend, Duff Intemann, so businesses could keep track of their vehicles.

It works like a basic Navman and has a GPS unit that tells the driver how fast the car is travelling and on what street but instead of displaying it on a screen in the car it sends it via a mobile data network - internet- to a server. The information is then stored in a database that can be accessed via the website.

Inspector Matt Rogers, of police northern communications centre, said there had been cases previously when commercial vehicles such as courier vans had provided similar information but the problem was that the lag between when the GPS co-ordinates were received could be up to five minutes.

He said the case demonstrated what police wanted to be able to do. "If it's happening here and now then we'll obviously divert as many resources as possible to catch an offender."