In March last year then Corrections Minister Judith Collins said a new ankle bracelet design was being introduced that would stop the small percentage of offenders from cutting off their electronic monitoring device and running from the law.
At the time she said: "It will be very, very difficult to cut these ones off."
Deputy national commissioner for the Department of Corrections Rachel Leota said the 3M company had strengthened the strap for the bracelets.
"The new strap is stronger and more resistant to being cut. All straps, including the new strengthened straps, are designed to meet international standards and must be able to be removed in an emergency."
Leota confirmed the strengthened straps were being fitted to offenders assessed as higher risk from July last year. However, for security reasons, Corrections would not comment on details around the construction of the bracelets.
Last year, Collins said a silicone module had been added to reduce false tamper alerts.
"If an offender removes or tampers with their anklet, an alert informs our monitoring staff and there is an immediate response."
Leota said police were advised and if the strap was cut, offenders could face penalties imposed by the court, including imprisonment.
About 3700 offenders and people on bail are being managed on electronic monitoring at any one time.
"Corrections had confidence in electronic monitoring as one element of our system for the management and supervision of offenders in the community."
Offenders on electronic monitoring have a compliance rate of just over 97 per cent.