Doors – How to install an electronic door lock

You don't necessarily need an electronic lock - you just need a lock that is always locked from the outside and yet allows exit from the inside. Something commercial in nature is probably in order. You probably won't find this at a home supply store, however. You likely will need to consult a locksmith.

CORRECTION

Link to Home Depot collection of storeroom locks.

You can find them at Home Depot.

Thanks to RSMoser for the proper name!

They've done the exact modification that you're proposing (placing it next to the door, rather than in the door) at my place of work.

What you're looking for is called an 'electronic strike'.

You cut out the area around the existing strike plate, and wire in the electronic strike. You'll need to feed it power, and a signal from whatever you have to grant access. (in our case, the card reader, plus a motion detector so it'll open from the inside automatically; you don't need the motion detector if you still have a functioning door handle from the inside)

A quick search online suggests that they run $100-500 (US$), but you'll probably want to contact the manufacturer of the card reader to ensure you get something that's compatible.

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As for 'best practice', much of it comes down to cost vs. what you're trying to protect.

The advantage of the electronic strike is that it can be hard-wired for power (no batteries to replace every few months), and you don't have to worry about cable bundles through the door or wireless signals (for auth & logging) that can be intercepted or interfered with.

If you're only protecting a single door (so don't have a centralized authentication server), don't need to log each person individually, and don't mind changing out batteries once in while, you might try looking at the locks they use for hotel room doors that replace out the existing handle + lock mechanism.