Under the deal, Ericsson will develop the force's national communication network and supply it with microwave radio systems and provide support to police radio sites.
However, Forrester Research's senior analyst Sam Higgins said the contract could pose an -innovation risk" because of its extraordinary length.
"I just don't know how you could get that [idea] through... In a contract that long, you're going to get innovation risk," said Higgins, who claimed he had never before come across a technology contract lasting 21 years.
"If I was the tax-paying public in New Zealand, I'd want answers on how we get value for money? What are the opt-outs for New Zealand police," he said.
One possible explanation for the length of the deal was multiple exit points for New Zealand police, according to Higgins. However, in telecommunications, this was still an extremely long time given the frequency of innovation in that field, he said.
Financial details of the contract were not disclosed and New Zealand Police did not respond to requests for comment.
According to a statement from New Zealand Police, although Ericsson already supplies mobile security software and IP telephony to the force, this is the longest deal it has ever signed with the vendor.