Announcing arrest is not legally required, according to some.
I don't know the Utah law on this - do you?
Utah Code 77-7-6. Manner of making arrest. (1) The person making the arrest shall inform the person being arrested of his intention, cause, and authority to arrest him. Such notice shall not be required when:
(a) there is reason to believe the notice will endanger the life or safety of the officer or another person or will likely enable the party being arrested to escape;
(2) (a) If a hearing-impaired person, as defined in Subsection 78-24a-1(2), is arrested for an alleged violation of a criminal law, including a local ordinance, the arresting officer shall assess the communicative abilities of the hearing-impaired person and conduct this notification, and any further notifications of rights, warnings, interrogations, or taking of statements, in a manner that accurately and effectively communicates with the hearing-impaired person including qualified interpreters, lip reading, pen and paper, typewriters, computers with print-out capability, and telecommunications devices for the deaf.
(b) the person being arrested is actually engaged in the commission of, or an attempt to commit, an offense; or
(c) the person being arrested is pursued immediately after the commission of an offense or an escape.
(b) Compliance with this subsection is a factor to be considered by any court when evaluating whether statements of a hearing-impaired person were made knowingly, voluntarily, and intelligently.