Smart lock installation basics: door thickness, mortise and backset

Most smart lock returns are fitment problems, not electronic failures. These are the numbers to collect before quoting, and to publish next to every product.

Door thickness

Every lock is designed for a thickness range — commonly 35–50 mm for residential mortise and deadbolt locks, with wider ranges for steel and security doors. A door outside that range needs different screws, a spacer or a different model. Measure at three points, because timber doors are not perfectly uniform.

Backset

The distance from the door edge to the centre of the lock or handle bore. It differs by market — 60/70 mm in Europe, 2⅜ or 2¾ inches in North America — and it is the single most common reason a replacement lock will not fit. Always quote it in the same unit as the customer's drawing.

Mortise pocket and faceplate

For mortise locks, the pocket size, faceplate dimensions and screw positions must match the existing cut-out, or the installer has to re-mortise the door. Ask for the faceplate drawing, not just a photo, and compare it with the door preparation.

Cross-bore, handles and strikes

• Cross-bore diameter and height above the floor
• Handle centre distance on mortise sets
• Strike plate dimensions and frame condition
• Whether the door is left- or right-handed and inward or outward opening
• Frame material and whether it can accept the strike and the wiring for any external module

Installer checklist

Before drilling: confirm thickness, backset, handing, and that the frame closes squarely. Test the lock with the door open before final fixing. Set the auto-lock delay appropriate to the site, and hand the customer the mechanical key and the app instructions in their language. These four steps remove most post-installation calls.