Police in Leicestershire are asking people to be wary of anyone offering to sell copper wire after a spate of thefts from electricity substations.
Officers said 10 substations across the county were hit during June.
Rising prices for copper have led to increased thefts nationally and regions are suffering from the knock-on effects of this trend, police said.
Pc Tiffany Lynch said people should heed "danger of death" signs at substations as thefts could be fatal.
"Thieves are not only exposing themselves to the risk of electrocution, they are also leaving these extremely dangerous sites open for children to wander into, with potentially fatal consequences," said Pc Lynch.
"It poses a serious threat to safety for electricity workers who enter an unsecured station after the thieves have gone."
Officers said they would be checking the identification of "any person that they reasonably considered it necessary to challenge in the vicinity of electricity cables, substations and metal dealers in the county".