Landlords who suspect houses they own may be being used as illegal cannabis "factories" are being warned not to try to force their way in to find out.
Devon and Cornwall police say properties may be booby-trapped and advise worried landlords to contact them first.
The advice comes after officers seized 1,500 cannabis plants from an address in Plymouth on Monday.
It was the largest cannabis factory found in the city so far.
"We have actually found Taser-style cattle prods in some of the premises"
The home, in Lockington Avenue, Plymouth, was raided by police on Monday night.
And on Wednesday another cannabis factory was found at a property in Cheltenham Place, Plymouth.
It was discovered, deserted, by a tradesman who had been asked to go round by the landlord.
Det Cons Mike Bradley, a drugs intelligence officer with Devon and Cornwall Police, said: "We're saying to landlords, please don't approach these places.
"In other parts of the country we have found booby traps. We don't want you to go forcing your way in.
"If you can't get into your premises, if the windows are all blacked out, and the locks have been changed and you're suspicious, please contact the police."
"We have actually found Taser-style cattle prods in some of the premises.
"People are going to try to protect their profits."
He said in other counties homes had been found with double-glazed doors wired up to the mains to prevent anyone coming in and stealing the crop inside.
Police have now raided 13 properties found to be growing cannabis in Devon and Cornwall and say they are "looking at" others.
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