Your analogy only works if the police
already have the key.
A warrant lets them search but it doesn’t automatically let them
compel me to help: I am being compelled to help them if they force my thumb onto the fingerprint scanner.
Also ‘testimonial’ isn’t limited to speech. Forcing biometric unlocking can communicate control/access in a way that courts can treat as testimonial.
This interpretation
is exactly what the D.C. Circuit did when they held that compelled thumbprint unlocking violates the fifth amendment.