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Lockpicking and the Internet
Start with keypads, more and more common on house doors. These have the benefit that you don't have to carry a physical key around, but there's the problem that you can't give someone the key for a day and then take it away when that day is over.
Keypads have other security failures, as well. I regularly see keypads where four of the 10 buttons are more worn than the other six. They're worn from use, of course, and instead of 10,000 possible entry codes, I now have to try only 24.
Fingerprint readers are another technology, but there are many known security problems with those. And there are operational problems, too: They're hard to use in the cold or with sweaty hands; and leaving a key with a neighbor to let the plumber in starts having a spy-versus-spy feel.
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