Salinas v. Texas

If you're not under arrest and police are questioning you, simply going silent when asked an incriminating question can be used against you unless you explicitly say "I invoke my Fifth Amendment right to remain silent."

A suspect's silence in response to police questioning before arrest can be used as evidence of guilt at trial if the suspect did not explicitly invoke the Fifth Amendment.

Always explicitly invoke your rights rather than just staying quiet. Outside of a custodial setting, silence alone is not protected.