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How to fit a smart door lock

Updated: 16 October 2026

You have a compatible UK door, a boxed lock, and a free Saturday. The job fails when the door already needs a shove before the key will turn, or when the box belongs to a different mechanism. This is how to fit a smart door lock for the Yale Conexis L2, the Nuki Smart Lock Pro, and a fingerprint lever in our [smart door lock](/hub/electronic-surveillance/smart-door-lock) comparison. The Products Compared editorial team used the manufacturers’ UK instructions and the amazon.co.uk listings captured on 15 October 2026. We did not fit these locks in a lab. A qualifying purchase can earn us a commission at no extra cost to you.

You have a compatible UK door, a boxed lock, and a free Saturday. The job fails when the door already needs a shove before the key will turn, or when the box belongs to a different mechanism.

Our top picks

Nuki Nuki Smart Lock Pro, retrofit, Wi-Fi

Best overall

Nuki Nuki Smart Lock Pro, retrofit, Wi-Fi
8.8/10about £229
View offer
TEKXDD TEKXDD fingerprint handle, matte black

Best value

TEKXDD TEKXDD fingerprint handle, matte black
8.6/10about £39.99
View offer
Yale Yale Conexis L2, chrome, with Wi-Fi bridge

Alternative

Yale Yale Conexis L2, chrome, with Wi-Fi bridge
7.2/10about £188.98
View offer
On this page
  1. 1.Test the door before you open the box
  2. 2.Measure thickness, backset, and both cylinder sides
  3. 3.Three fits in this set
  4. 4.Backup power and the first week

Test the door before you open the box

Yale’s Conexis L2 manual asks you to prove the existing lock before the handle comes off. With the door open, lift the handle fully and turn the key. Close the door, lift the handle fully, and turn the key again. Both turns should be smooth. If the key turns only when you lift the door on its hinges, or push the leaf into the frame, stop. Locks & Alarms, a UK trade page, makes the same stop: the door has to close and lock cleanly before a smart unit goes on. If you are no longer sure which product you bought, check the format on the smart door lock buying guide.

Measure thickness, backset, and both cylinder sides

Thickness is the full leaf at lock height, in millimetres. The Conexis listing states PVC and composite doors of 44–70 mm. The TEKXDD states 35–55 mm. Both Yale Keyless listings are described around a 60 mm backset, measured from the latch face to the centre of the spindle. For a euro cylinder, measure the inside and the outside separately from the fixing screw in the edge. The Nuki Ultra replaces the cylinder, so those lengths decide whether the new one sits flush. Nuki splits the Pro mount: a screw-on plate if the cylinder overhangs by at least 3 mm, and a stick-on plate if it stands proud by less.
Nuki Nuki Smart Lock Pro, retrofit, Wi-Fi

Testsieger

Nuki Nuki Smart Lock Pro, retrofit, Wi-Fi
8.8/10about £229
View offer

Three fits in this set

The Conexis L2 replaces the handle on a lift-to-lock door. You lock it by lifting the handle until the motor stops. If the tailbar will not reach, that is the locksmith moment. The Nuki Pro goes over the cylinder you keep. Put the key in first. With the inside key inserted, the outside key must still operate the lock. Nuki calls that the emergency function, and the compatibility guide limits the key to about 4 mm thick and 37 mm of protrusion. Leave the inside key in place. The Ruveno is a lift-to-lock handle with a 3585 mortise, a professional fit recommended in the bullets, and a review that describes a cable hole between the two halves. If you cannot see that your case is a 3585, stop. The choice between Conexis and Nuki is on Yale Conexis vs Nuki.

Backup power and the first week

Yale’s UK tenant page for the Conexis, rather than the amazon.co.uk bullets for this ASIN, describes four AA alkaline cells, about a year of use, and a 9 V battery on the outside if they fail. The Ultra and the Pro use a rechargeable pack and a magnetic charging lead. The TEKXDD’s four AAA cells are not in the box, and the listing claims 6–9 months. Call a locksmith for a dropped door, a mortise you cannot identify, a fire door, or a rented final exit you are not allowed to alter. If this door is the one in your policy, read smart lock home insurance before you drill.

Common questions

What do I test before I remove the old handle?
Lift the handle fully and turn the key with the door open, then do the same with the door closed. Yale’s Conexis L2 manual treats a stiff turn as a stop, and says a locksmith may be required. A nightlatch should throw without you lifting the door on its hinges. A motor on a door that already binds will stall.
How do I measure a euro cylinder?
Measure each side from the fixing screw in the edge, inside and outside separately, because the lengths often differ. Thickness is a different figure: the full leaf at lock height. Backset, for the 60 mm Yale nightlatch keypads, runs from the latch face to the centre of the spindle.
Does the Nuki Pro need the key left inside?
Yes. The key goes in before you mount the lock, and it stays on the inside. With that key inserted, the outside key must still work. Nuki’s compatibility guide limits the key to about 4 mm thick and 37 mm sticking out. If the outside key stops once the inside key is in, the cylinder lacks the emergency function this retrofit needs.
How do I lock a Conexis L2?
Lift the handle fully and hold it until the motor stops. That is Yale’s instruction, and Which? describes lift-to-lock the same way: you still lock by hand. Unlock with the app, a key tag, or a key card. This ASIN includes the Wi-Fi bridge.
What powers the lock if the batteries are flat?
Yale’s UK Conexis page describes a 9 V battery on the outside, and four AA cells day to day. That 9 V line is Yale’s, not an amazon.co.uk bullet on this ASIN. The Nuki Pro and Ultra use a rechargeable pack, and the Ultra’s box includes a magnetic charging cable.
When do I stop and call a locksmith?
Stop when the key will not turn cleanly open and closed, when the door has dropped, when you cannot identify the mortise, when the door is a fire door, or when you rent and the final exit is the landlord’s. Also stop if a Conexis tailbar will not align, or if a Ruveno case is not the 3585 mortise in that box.

Related pages

Best smart door locks

Smart door lock

Smart door lock buying guide: match your mechanism

Smart lock home insurance: ask before a cylinder swap

Yale Conexis vs Nuki: handle, Pro, or new cylinder

Sources

Public UK sources for the standards, insurance wording, and product-security rules, last checked on 15.10.2026. Prices and star ratings are the amazon.co.uk figures captured that day.

  1. GOV.UK: Regulations for consumer connectable product security (retrieved 15.10.2026)
  2. Product Security and Telecommunications Infrastructure (Security Requirements) Regulations 2023 (retrieved 15.10.2026)
  3. Allianz UK: Stay insured with the right house locks (retrieved 15.10.2026)
  4. MoneySuperMarket: What locks do I need for home insurance? (retrieved 15.10.2026)
  5. Secured by Design: Locks and associated hardware (retrieved 15.10.2026)
  6. Yale Home: Compatible with Conexis (retrieved 15.10.2026)
  7. Nuki Help: What is the emergency function? (retrieved 15.10.2026)
  8. Which?: Do I need a smart door lock? (retrieved 15.10.2026)