Seriously, everybody knows about the doormat.
Maybe under the doormat was a fine place to hide a key a few decades ago (but probably not). It’s also possible that fake rocks were secure when the first 1,000 people tucked their keys inside and hid them in the dirt. And the top of door frame is still an ideal place to stash a key if your know all prospective burglars are under 4 feet (1.2 meters) tall and have no access to a ladder.
But if it’s the 21st century, and if you’re would-be thief is post-pubescent, you’re going to have to step up your practical management. When you hide your spare house key in an obvious place, you may be reducing your inconvenience in the case that you lock yourself out or need a friend to pick up the mail when you’re gone, but you’re increasing the chance you’ll find yourself in the much more inconvenient position of being robbed.
It’s best not to have an extra key anywhere on your property. The safest place for a spare key is with a trustworthy neighbour or two or your security company.
If you must hide one, be creative. If your friends can guess your hiding place on the first try, pick a new one.
If you’re constantly locking yourself out, you might just chuck the key and invest in a keypad or fingerprint door lock. Thieves will have a harder time locating your spare when you’re away.