1. Identify the lock type before shopping

Start with the door or window material and the existing hardware. uPVC and composite doors often use euro cylinders and multipoint mechanisms, while timber doors may use mortice locks, night latches or a combination.

• Check whether the lock is part of a multipoint system.
• Look at handle compatibility, fixing positions and door thickness.
• For windows, check whether the lock affects an escape window.
• Photograph the existing hardware for comparison, without sharing keys or sensitive details publicly.

2. Measure cylinders and hardware carefully

Euro cylinders come in different internal and external lengths. The wrong size can look untidy, fail to fit or reduce security. Measure from the fixing screw position to each face of the handle or escutcheon, and check whether you need a thumb-turn, key-key or keyed-alike option.

• Measure both sides; they are not always equal.
• Check the finish and handle depth, not just the door thickness.
• Choose appropriate security ratings for external doors.
• Do not rely on guesswork for insurance-sensitive doors.

3. Balance security with escape routes

A stronger lock is not automatically better if it makes daily use awkward or blocks emergency exit. Think about children, visitors, older people, accessibility needs and whether keys are likely to be available when needed.

• Consider thumb-turn cylinders on suitable escape doors.
• Do not lock emergency egress windows in a way that prevents escape.
• Keep spare keys secure but accessible to the right people.
• Review locks alongside smoke alarms, lighting and household routines.

4. Know when to use a locksmith

Buying the part is only half the decision. If the door is misaligned, the multipoint gearbox is stiff, the frame is damaged or insurance wording is specific, a locksmith can save money by diagnosing the system before parts are ordered.