N.H. Rev. Stat. Ann. § 266:73

It shall be unlawful for any motor vehicle to be driven on the ways of this state equipped with a siren. The provisions of this section shall not apply to such emergency vehicles as police, fire department, fire patrol, state department of corrections vehicles, retired fire apparatuses as defined under RSA 259:4, nor to those law enforcement officers or volunteer members of fire departments nor to public or private ambulances.