A sharp decline in metal theft has been cautiously welcomed by police, who recognise opportunists could strike at any moment as markets fluctuate.
Figures for March 2018 to 2019 showed scrap metal theft incidents across Suffolk fell to 181 from 310 the previous year.
It followed a two-year resurgence in crimes across much of England after consistent falls between 2013 and 2016.
Offences had halved in the three years after the 2013 Scrap Metal Dealers Act made it harder to sell stolen components.
Last year saw the lowest number recorded since the Act came into force, but Sergeant Brian Calver said the rural crime team had seen a recent spike - possibly due to an increase in the value of certain commodities.
"Like a lot of things, it's less attractive to criminals when it's of less value - it's simple supply and demand," he added.
"We know that disrupting their activity has a significant impact on their finances."
Last year's decline was largely influenced by a drop in domestic metal theft of items like gates and fencing (from 252 to 127), while infrastructure related theft of items like lead from public buildings remained stable.
It had been suggested that the preceding rise was down to limited enforcement of the 2013 Act, which Sgt Calver said yards were now mostly compliant with.
He added: "To those in charge of infrastructure, we suggest they review their security and have the best they can afford.
"An awful lot of scrap metal thieves are opportunists, so we urge farms and industrial premises to follow simple practices like locking gates.
"It's the same for plumbing and heating engineers who might store old hot water tanks on their properties before taking them to the scrap yard.
"The vast majority of stolen metal is taken to yards to be got rid of by those that don't ask questions.
"The Act requires records to be kept and allows us to link things like registration plates of vans back to where it happened.
"We can then make arrests, recover and confiscate money from them as proceeds of crime.
"We've had some good results recently, but it's easy to get complacent, especially when things like church roof thefts have gone down.
"If people aren't alert, it can happen again suddenly."
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