Four sat-navs have been stolen after a spate of thefts in Abbots Langley and Kings Langley on Wednesday night.
Hertfordshire Constabulary are treating four thefts from cars as linked after four sat-navs and a number of other items, including sun glasses and prescription glasses, were taken between 8pm on Wednesday, August 20 and Thursday, August 21.
Officers said that an offender, or offenders, were gaining entry into the parked cars through "unknown means" despite all of the cars being locked.
A green Ford Focus was broken into in Station Approach, Kings Langley, where a sat-nav, three pairs of sunglasses and a large bottle of engine oil were taken.
Offender(s) also gained entry into a Blue Seat Ibiza, which was parked in Gallows Hill Lane, Abbots Langley and two sat-navs were stolen, including the one built into the car.
A Tom-Tom sat-nav, an MP3 player, a pen knife and a USB stick were taken from a blue Seat Altea, from Lauderdale Road, Hunton Bridge.
Polo mints, a pair of driving prescription glasses, a blue disabled badge, a gate key and two pairs of sunglasses were also taken from a blue Ford Fiesta from another car parked in Lauderdale Road.
Police are asking for anyone to contact them if they have information, particularly if they are being offered cheap sat-navs or other items that were taken.