Summary
Smart locks are sold as a plug-and-play consumer product, but the fitting itself still follows the rules of traditional lock work — correct measurement, correct backset, correct door preparation — with an added layer of electronics configuration on top. Tradespeople coming from a locksmith or general carpentry background need to add battery, connectivity and app-pairing steps to their process. Tradespeople coming from an electrical or smart-home background need to add door hardware measurement and mechanical compliance to theirs.
The most common fitting failures aren't electronic — they're mechanical. A retrofit device fitted to a door that's slightly out of alignment will bind, drain the battery faster (the motor works harder against friction) and eventually fail to lock. A cylinder ordered to the wrong backset either won't engage the gearbox cams or will protrude and be vulnerable to snapping. Get the door right first, then configure the electronics.
The second most common failure is leaving the customer without a reliable way in if the smart function fails — flat battery, app outage, or a paired phone left at work. Every installation should end with the customer holding a demonstrated, working backup: a physical key, a mechanical code, or a documented recovery procedure.
Key Facts
- Backset (distance from the door edge to the centre of the cylinder/keyhole) is the most common wrong-order mistake — measure before ordering, don't assume a standard size.
- Euro cylinder sizing is given as two numbers either side of the fixing screw (e.g. 35/45mm) — measure both sides independently as they're often unequal on entry doors.
- Door thickness determines whether a retrofit device's internal mechanism will clear the door edge and reach the thumbturn spindle without modification.
- Mortice lock case depth (for wooden door deadbolt replacements) must match the existing pocket, or new joinery work is needed — check before quoting a fixed price.
- Connectivity protocols: Bluetooth (phone-proximity unlock, no hub, shortest range), Wi-Fi (direct internet connection, higher battery drain, remote access without a bridge), Zigbee/Z-Wave (mesh network, needs a hub, lower power draw), Matter (interoperability layer sitting over Wi-Fi/Thread, increasingly the default for new multi-ecosystem installs).
- Auto-relock — most smart deadbolts default to relocking after 5–30 seconds; confirm the customer's preferred delay during handover, as too short a delay causes nuisance re-locks on people carrying shopping.
- Battery type and life — typically 4× AA or a proprietary lithium pack, rated 6–12 months of typical use; always fit fresh batteries at handover and show the customer the low-battery warning method (app alert, audible beep, or external contact-charging pins).
- External power backup — many keypad units have 9V battery terminals or USB-C emergency power contacts on the exterior faceplate for when the internal batteries die; demonstrate this at handover.
- Fire door hardware — front doors to flats and doors onto protected escape routes need CERTIFIRE-listed (or equivalent tested) hardware; do not substitute an untested smart mechanism.
- Self-closing device compatibility — communal fire doors with an overhead closer need a smart lock rated to cope with the closing force and cycle count; standard retrofit devices are not always rated for this duty.
- Weatherproofing (IP rating) matters for external keypads exposed to driving rain — check the manufacturer's IP rating before fitting to an unsheltered door.
- App and network handover — set the smart lock up on the customer's own account, not an installer account, and remove any temporary installer access codes before leaving site.
- Multi-user access — for shared households, HMOs or holiday lets, set up individual codes/credentials rather than one shared code, so access can be revoked individually later.
Quick Reference Table
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Try squote free →| Step | What to check/do | Common failure if skipped |
|---|---|---|
| Door survey | Thickness, backset, cylinder length, mortice depth | Wrong part ordered, second visit |
| Door alignment | Door closes square, no binding on the frame | Motor strain, premature battery drain, jamming |
| Mechanical compliance | BS 3621 / TS 007 rating maintained | Insurance claim risk for customer |
| Power source | Fresh batteries fitted, external backup terminals tested | Lockout on day one |
| Connectivity | Correct protocol chosen for customer's ecosystem/hub | Device unusable with existing smart home setup |
| Network setup | Customer's own Wi-Fi/app account used, not installer's | Access control lost after installer leaves |
| Auto-relock timing | Set to customer's usage pattern | Nuisance relocking or door left unlocked |
| Backup access | Physical key or master code demonstrated and tested | Total lockout if electronics fail |
| Multi-user setup | Individual codes/credentials per household member | Cannot revoke single user's access later |
| Fire door check | CERTIFIRE/fire-rated hardware confirmed if applicable | Non-compliant fire door, landlord liability |
Detailed Guidance
Surveying the door before ordering hardware
Before specifying any smart lock, take four measurements: door thickness, cylinder backset, cylinder length on both sides of the fixing screw, and — for wooden doors — the mortice case depth and the distance from the door edge to the centre of the keyhole (backset). Photograph the existing lock face and cylinder end so the fitting can be matched exactly if a site visit isn't practical before ordering.
Check the door's alignment in its frame while you're there. A door that needs a firm shove to latch will cause a motorised smart lock to draw excess current fighting the friction, shortening battery life dramatically and sometimes preventing the bolt from throwing at all. Fix hinge or frame alignment issues before or as part of the smart lock job — don't fit a smart mechanism to a badly hung door and expect it to work reliably.
Fitting retrofit devices (no cylinder replacement)
Retrofit devices clip over the existing thumbturn and drive it electronically, leaving the original mechanical lock and its BS 3621/TS 007 rating untouched. Confirm the thumbturn shape and depth match the device's adaptor before fitting — most come with a set of adaptor collars for different thumbturn profiles. Mount the outer bracket square and level; a device mounted slightly off-axis will bind against the thumbturn under motor load.
Fitting smart cylinders and multipoint mechanisms
A smart cylinder replaces the entire cylinder barrel — measure and order to the exact backset (both sides) before removing the old one, and never leave a door without a working cylinder overnight. For multipoint mechanisms (UPVC/composite doors), the gearbox itself is replaced — this needs the door to be off its hinges or the mechanism accessed via the edge of the door, and is the job most likely to need a second person or extra time if the existing gearbox is a non-standard length.
Connectivity setup and hub requirements
Decide the connectivity protocol before the visit, based on what the customer already has: if they run a Zigbee or Z-Wave smart home hub, match the lock to it rather than adding a competing Wi-Fi device. If they have no existing smart home ecosystem, Bluetooth-only units avoid the complexity of a hub and network credentials, at the cost of no remote/away-from-home access. Matter-compatible devices are increasingly the safer choice for a customer who may add other ecosystem devices later, since Matter is designed to work across Wi-Fi and Thread network types rather than being tied to one manufacturer's hub.
Handover: backup access and code management
Never leave a job without demonstrating the backup access method — physical key override, external power terminals, or a documented recovery code — in front of the customer. Remove any installer-level access code or pairing before leaving, and confirm the smart lock is registered to the customer's own account rather than a temporary one. For multi-occupancy properties, set up separate codes per person so individual access can be revoked without re-keying the whole lock.
Fire doors and communal entrances
Front doors onto communal stairwells in flats, and any door on a designated escape route, are usually fire doors with certified hardware. Fitting a standard retrofit or replacement smart lock to a fire door without checking its fire test certification is a compliance and liability risk — check the door's fire rating and the smart lock manufacturer's fire door certification (or the lack of one) before quoting the job.
Frequently Asked Questions
Will a smart lock work if the power or Wi-Fi goes down?
Battery-powered units keep working on local power regardless of the home Wi-Fi or internet connection — Bluetooth and most Zigbee/Z-Wave functions operate locally. What stops working is remote/away-from-home access via the app, and any cloud-dependent feature like voice assistant integration. Always confirm the customer understands the difference between local (battery-only) function and remote (internet-dependent) function.
Can I fit a smart lock without replacing the existing cylinder?
Yes — retrofit devices are designed exactly for this, clipping over the existing thumbturn and driving it electronically while leaving the original mechanical lock and its insurance rating in place. This is the fastest and lowest-risk installation category, and the right recommendation for most customers who don't specifically need remote/keypad access on the outside of the door.
How do I stop the smart lock draining its batteries too fast?
The most common cause is a misaligned door forcing the motor to work harder than it should on every lock/unlock cycle. Fix hinge and frame alignment first. After that, check whether frequent app polling or a weak Wi-Fi/Bluetooth signal at the door is causing the unit to retry connections repeatedly, which also drains batteries faster than the manufacturer's rated life.
Do I need a separate hub for every smart lock?
No — it depends on the protocol. Bluetooth-only locks need no hub. Wi-Fi locks connect directly to the home router. Zigbee and Z-Wave locks need a hub (either a dedicated one or a smart home hub that already supports the protocol) to bridge them to the internet and app. Choose based on what connectivity the customer already has in the house, not a default preference.
Regulations & Standards
BS 3621 — mortice deadlock standard for wooden doors; must be maintained if the smart lock replaces or works alongside the mechanical deadlock.
TS 007 — euro cylinder security rating (1–3 star) for UPVC/composite doors.
Sold Secure Diamond (SS312) — enhanced cylinder test standard exceeding TS 007, confers Secured by Design status.
BS EN 179 / BS EN 1125 — panic and emergency exit hardware standards for doors on escape routes.
CERTIFIRE — third-party fire test certification scheme for door hardware fitted to fire doors.
Part P, Building Regulations (England & Wales) — applies only if the job includes new fixed wiring for a mains-powered hub, access panel, or power supply.
DHF | TS 007 — official TS 007 standard reference
What Types of Door Locks Do I Need For Insurance? | Lemonade UK — insurer security standard requirements
Comparing Secure Diamond Cylinder Locks | Doorfit — cylinder rating comparison
Smart Locks & Video Doorbells: UK Buying Guide 2026 | LocksmithLocal — connectivity and installation considerations
smart lock installation pricing guide — labour, materials and margin for quoting this job
home automation protocols — Bluetooth/Zigbee/Z-Wave/Matter comparison for connectivity decisions
part p notifications — when electrical work on a smart home job becomes notifiable
smart home fault — diagnosing connectivity and pairing faults on smart home devices