Two people have been cautioned for using wireless broadband connections without permission.
A man was arrested in Redditch, Worcestershire, on Saturday after residents spotted him using a laptop while parked in his car outside a house.
A 29-year-old woman was arrested following a similar incident, also in Redditch, this month, but officers do not believe there is any link between the pair.
Both have been cautioned for dishonestly obtaining electronic communications services with intent to avoid payment.
Pc Tony Humphreys, from West Mercia Police, said: "We want people to be aware that this is possible.
"Wireless networks don't stop at the walls of your home - and so without the necessary protection, your neighbours or people in the road outside may be able to connect to your network.
"This might slow down your internet service, or more importantly, your internet connection could be used for unlawful purposes."
Most wireless networks are unsecured when first set up, but can be configured to stop unauthorised users accessing them.
Pc Humphreys added: "We do not want to alarm wireless broadband users - we want them to follow the advice on wireless broadband security issued to them by their broadband providers."
It is believed these incidents are among the first cases of "wi-fi theft" in the UK.
