Rim nightlatch (surface-mounted)
A surface-mounted case on the inside of the door with a cylinder through the door face. Pulling the inside knob retracts the latch; the outside is key-only. Universally fitted, cheap, and mechanically simple — but the case geometry varies more than any other family.
Also called: Yale lock · Night latch · Rim lock
Anatomy
- Surface case on the inside face
- Rim cylinder screwed through the door
- Inside knob or handle
- Spring latch, sometimes deadlocking
Parameters to measure
Measure in this order: Lock case width × height × depth → Backset (Dornmaß) → Interior thumb-turn / turn-piece size and profile → Door thickness
| Parameter | Typical values | Tolerance that still fits | How to measure |
|---|---|---|---|
| Lock case width × height × depth | Case widths 60–90 mm; heights 60–100 mm | Survey before designing | Width and height of the surface case. |
| Backset (Dornmaß) | 60 mm typical | — | Door edge to the centre of the rim cylinder. |
| Interior thumb-turn / turn-piece size and profile | Round knob 25–35 mm, or a lever | — | Measure across the knob and note the fixing. |
| Door thickness | 35–55 mm | — | At the cylinder. |
Retrofit architectures that work
- Motor on a rim (surface-mounted) lock — A motor unit is fixed to the surface-mounted rim lock case or to its knob, driving the latch or the deadbolt. Common on UK nightlatches and on Asian surface-mounted deadlocks.
- Surface motor on a deadbolt turn-piece — An adhesive or screw-fixed motor sits on the door face and rotates the existing deadbolt turn-piece. Nothing is drilled. This is the standard approach for North American single-cylinder deadbolts and for many Asian rim deadbolts.
The spring is the enemy: retracting a spring latch under motor drive takes more torque than turning a deadbolt, and the duty cycle is high. Expect poor battery life unless the design adds a clutch.
Related standards
Reference devices
Recorded as engineering examples, not endorsements.
- SwitchBot Lock Pro — Surface motor on a deadbolt turn-piece ✓ verified
Questions
Is a nightlatch enough on its own?
No. Insurers expect it alongside a 5-lever deadlock on a timber front door, because a spring latch can be slipped with a card.
Can a motor drive the inside knob?
Yes, that is the usual approach — a clamp and motor on the knob. The adapter must tolerate the knob being off-centre relative to the case.