Definitely make sure you think through all the physical security implications of having your house automatically unlock in any scenario.
Have the house auto unlock when getting home on a bicycle, sounds convenient until, as you point out, they could get stolen and now the thief has a convenient way to unlock your house. So you would not want that.
You would definitely not want the house to STAY unlocked when something like a tag is in range. If your kid is home alone, you want them to be able to re-lock the house (or in general, you want to be able to lock your house while the kid is home).
Whatever solution you wind up with, you are going to be trading physical security for ease of use (and complicated fun task). Be safe. Make sure the tradeoffs are actually thought through and worth it.