We knew our top pick would have to be "The Rock" of traditional locks: big, tough, and unmovable. The Medeco M3's solid, hardened steel construction and unpickable locking mechanism checked all the boxes. We especially liked that the unique lock style means unique keys, making them hard to duplicate. But keep in mind that if you need a duplicate key, or if you ever need to get the lock re-keyed, its uniqueness means you'll have some hoops to jump through.
The M3 lock is available in a variety of different finishes, and it comes with a high-security, box-style strike plate with two-inch, high tensile screws—not as long as the three-inch screws we prefer for a truly secure door, but better than the standard one-inch. Installation can be difficult, so you might want to have a locksmith on call just in case. You can order several Medeco locks for your home and have them keyed the same or differently.
The price tag on the M3 is definitely higher than the other locks on our list, but for everything it offers in protection, we think the triple-digit price is well worth it.