Two people have been cautioned for using people's wi-fi broadband internet connections without permission.
Wireless networks at home give people freedom
Neighbours in Redditch, Worcestershire, contacted police on Saturday after seeing a man inside a car using a laptop while parked outside a house.
He was arrested and cautioned. A woman was arrested in similar circumstances in the town earlier this month.
BBC Midlands Today correspondent Dr David Gregory said the cases are among the first of their kind.
He added that if people were using someone else's network to enter illegal porn sites, for example, it would be very difficult to trace them.
The man arrested at the weekend was cautioned for dishonestly obtaining electronic communications services with intent to avoid payment.
In the earlier incident, a woman was arrested after attracting the attention of neighbours in the early morning.
She had put up cardboard around her car windows but the light from her computer could be seen through the back window.
West Mercia Police said people with wi-fi should follow security advice given by their internet provider.
ISPs recommend that wi-fi users secure their wireless networks.