TexasCHLforum.com

The lights and sirens on a police vehicle as a rule do not have to be activated for it to be an emergency vehicle. § 546.003-546.004 lists exceptions to when a police officer has discretion when using these devices even when involved in emergency response.

§ 541.201. VEHICLES. In this subtitle:
(1) "Authorized emergency vehicle" means:
(A) a fire department or police vehicle;
(B) a public or private ambulance operated by a
person who has been issued a license by the Texas Department of
Health;
(C) a municipal department or public service
corporation emergency vehicle that has been designated or
authorized by the governing body of a municipality;
(D) a private vehicle of a volunteer firefighter
or a certified emergency medical services employee or volunteer
when responding to a fire alarm or medical emergency;
(E) an industrial emergency response vehicle,
including an industrial ambulance, when responding to an emergency,
but only if the vehicle is operated in compliance with criteria in
effect September 1, 1989, and established by the predecessor of the
Texas Industrial Emergency Services Board of the State Firemen's
and Fire Marshals' Association of Texas; or
(F) a vehicle of a blood bank or tissue bank,
accredited or approved under the laws of this state or the United
States, when making emergency deliveries of blood, drugs,
medicines, or organs.