After a recent judge ruling, the ultra-secure fingerprint login feature your smartphone may offer doesn't seem quite so secure after all. Virginia Beach Judge Steven Frucci has ruled that while a person does not have to hand over their phone's passcode so that law enforcement can gain entry, a fingerprint is fair game.
Passcodes fall into the same category has passwords; both are considered 'knowledge'. Under the Fifth Amendment, you're not required to divulge personal information like that. Fingerprints are different story; they fall into the same category as DNA, a person's handwriting, or a physical key. Ultimately, this means that if you secure your phone with a fingerprint, and happen to have a run-in with the law, don't be surprised if you're asked to unlock it.
This ruling stems from a case earlier this year where a man was charged with strangling his girlfriend. Law enforcement were adamant about the fact that video of the argument that preceded the physical fight could be found on the phone. It's not entirely clear if the charged man was securing his phone with a fingerprint, but nonetheless, it's led to this.
If you're unhappy with this ruling and would like to keep your phone pretty-much inpenetrable from others, the best solution would be to make use of fingerprint security and a passcode; effectively securing your device with dual-protection. That way, a fingerprint might get appease the law, but you'd still be protected because of the passcode.