Billings police are warning motorists about suspicious explosive devices placed on roads in town.
Lt. Matt Lennick wrote on social media that police have identified seven incidents over the past few months, with the most recent Thursday night.
The devices are made of tinfoil wrapped around an unknown type of flammable material that ignites when run over, according to Lennick.
No one has been injured, and no property damage has been reported, Lennick wrote.
He urged drivers to be wary of items in the roadway and notify police of anything suspicious.