A home robbery gang used sticky tape on front doors to highlight potential targets in the Costa Blanca and Murcia areas.
The four-strong Georgian crew was tracked by the Policia Nacional in a surveillance operation.
Crew members stuck tiny pieces of barely-visible transparent tape on front doors.
If the tape was still there a few days later, it meant the property was empty with no occupants to concern the robbers during a break-in.
Policia Nacional patrols patiently lay in wait in Elche districts that saw recent rises in home burglaries.
The thieves, aged 37 to 59, drove one night from Torrevieja to Elche and were arrested leaving a building they had just robbed.
Several bags containing stolen loot like jewellery, watches and cash were seized along with tools to force door locks.
The police probe is still active as some residents may not know they have been robbed until look for a specific item of jewellery
The Policia Nacional says people should regularly check doors and locks for any suspicious markings that might act as a code for potential burglars.