Not to bag on the iPhone's fingerprint detection in general - it looks to be impressive to me, in fact - but one thing it probably won't do very effectively is

Not to bag on the iPhone's fingerprint detection in general - it looks to be impressive to me, in fact - but one thing it probably won't do very effectively is protect you from your spouse, or anyone else who has access to your hands while you sleep. The same risk will be present during overnight stays in police cells, probably.