Identify a UK Oval Cylinder and Night-Latch Boundary

A UK oval cylinder and a rim or night latch can be confused when you look only at the outside keyhole. Identify the cylinder profile and the lock body separately: one describes the cylinder shape, while the other describes the mechanism mounted in or on the door.

Illustrative arrangements only, not to scale. A door can have more than one lock or a mixed arrangement.

Look at both sides and the door edge

An oval cylinder is a profile visible at the door face; it may operate a lock body fitted into the door edge. A rim or night-latch case is mounted on the inside surface of the door, with its own latch mechanism. The visible cylinder or outside keyhole alone does not establish which body it operates or whether another lock is present.

Photograph the outside face, inside face, door edge, cylinder markings, handles, and any separate surface-mounted case. With the door open, use the normal key and handle actions without force. Record whether the key turns a deadbolt, the handle retracts a latch, or more than one action is needed. Do not remove the cylinder or case just to identify it.

These views help identify the arrangement; they do not prove that a smart lock fits or operates it.

Treat product lists as product-specific

Aqara’s U200 announcement names UK oval cylinders among several supported profiles. It also describes an emergency-function condition for the U200 Euro-mortise path. Those statements do not establish support for every oval cylinder, lock body, or combination of hardware; check the current instructions for the exact product and market.

Yale UK’s Linus support page links a compatibility checker for the mechanical lock and cylinder on the door. Yale also says its Linus kits are market-region specific. Use the UK checker and exact UK model information; do not transfer a result from a different market or treat an uncovered rim/night-latch arrangement as a confirmed fit.

If the door has both an oval cylinder and a rim case, or the normal operation does not identify which mechanism the proposed device would control, leave the result unknown. Continue with the mortise and latch-action guide and compatibility checklist, or ask the lock maker or a qualified locksmith to identify the mechanism.