Detectives in the metro area are warning people who rent storage units that their units could have been turned into clandestine meth labs if renters haven't checked on their belongings in a while.

Over the past several weeks, North Metro Task Force detectives have uncovered four meth lab sites in storage lockers in Westminster and unincorporated Adams County. Similarities between the cases indicate one person or group is responsible, the Broomfield Police Department said.

In most of the cases, storage lockers have been broken into, the hazardous items placed inside and the lock replaced.

The hazardous items included 5-gallon water bottles filled with unknown two-layered liquids that are both unstable and explosive. The liquids are extremely dangerous, senstive to heat and shock, and may explode if moved.

In the recent cases, the hazardous items were placed in a Dumpster that was on private property, but accessible to the public, police said. The Jefferson and Adams county bomb squads were called in to destroy the explosive items.

The North Metro Task Force believes there are more of these meth lab sites and wants to make the public aware of what's happening.

"If you rent a storage unit, please check your lockers to make sure the lock on it is yours. If there's a different lock on your storage locker, or if the lock is missing, do not open the locker to check its contents. Instead, contact your local law enforcement agency immediately," Broomfield police said.