Retrofit or full-replacement smart lock: how to choose
Updated
A retrofit lock keeps your existing deadbolt and key; a full replacement swaps the whole lock for a keypad version. Compare security, looks, rental fit and price before you choose.
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Which one should you pick?
A retrofit lock replaces only the inside thumbturn, so the outside cylinder and key stay and the original parts go back at move-out.
A full replacement includes the outside keypad and the bolt, so it is one product with one grade.
Retrofit keeps the hardware you already trust and adds smart control inside.
A full replacement has a keypad built in; a retrofit lock can pair with a wireless keypad accessory.
Retrofit vs Full replacement
| What changes | Retrofit | Full replacement |
|---|---|---|
| What changes on your door | Only the interior thumbturn and housing; outside cylinder stays | The whole deadbolt, inside and outside, including the key cylinder |
| Existing key | Keeps working | Replaced by new keys (rekey possible) |
| Keypad on the outside | Not built in; add a wireless keypad accessory | Built in on most models |
| Security rating | Depends on your existing deadbolt: check its ANSI/BHMA grade | Look for an ANSI/BHMA grade on the lock you buy |
| Appearance | Looks like your old lock outside; bulkier housing inside | New exterior design, uniform finish |
| Rental friendliness | Usually the easiest to get approved; no new holes | Landlord needs a key or code; ask first |
| Installation | Screwdriver; about 10 to 20 minutes if the thumbturn fits | Screwdriver; about 20 to 40 minutes; door must match standard prep |
| Door fit limits | Needs clear space around the thumbturn; double-cylinder locks do not work | Needs correct thickness and backset; handle clearance |
| Typical price | $100–$280 | $90–$300 |
How each type works
A retrofit smart lock removes only the interior part of your existing single-cylinder deadbolt, the thumbturn, and replaces it with a motorized unit that turns the same spindle. The key from outside still works because the cylinder and bolt never leave the door. A full-replacement smart lock removes the entire deadbolt and installs a new set: bolt, outside cylinder or keypad, and inside housing. See will a smart lock fit my door for the measurements both types require.
Security: the bolt and the door still matter
A retrofit lock is only as strong as the deadbolt you already have. If that deadbolt is a low grade or a weak cylinder, the smart part will not fix it. A full replacement lets you choose a lock with an ANSI/BHMA grade. Grade 1 is the highest, Grade 2 is described as excellent for most residential applications and Grade 3 is the minimum acceptable for residential locks. Either way, the frame matters: police guides recommend a throw of at least 1 inch and strike plate screws 3 inches long. Our smart lock safety guide covers accounts and settings.
Keypads, guests and daily use
Many retrofit locks have no keypad. If you want codes for the dog walker or a family member without a phone, buy the wireless keypad accessory or choose a full replacement. A keypad on the door also gives you a way in if your phone is dead. Full replacements also usually include a backup key cylinder; retrofit locks keep the one you already have.
Renting or sharing a door
If you rent, retrofit is the usual choice. Read smart lock for renters before you ask the landlord. If you have a disability and need a lock you can operate, the Fair Housing Act allows reasonable modifications at your expense, and the landlord can ask you to restore interior changes where that is reasonable.
When to switch from retrofit to full replacement
Change if you move into a home you own, if your old deadbolt is worn or low grade, if you want a keypad as the main way in or if the thumbturn clearance is too tight. Keep the retrofit lock’s key and spare parts in case you rent again.
Shop by need
Renter or owner keeping the existing deadbolt
What to look for: retrofit unit that supports your deadbolt brand style, door-position sensor, replaceable batteries, removable without tools beyond a screwdriver
Typical price: $100–$280
See options on AmazonOwner wanting a keypad as the main entry
What to look for: smart deadbolt with ANSI/BHMA grade, keypad, key cylinder backup, supported thickness range
Typical price: $90–$300
See options on AmazonRetrofit lock plus keypad
What to look for: wireless keypad paired with your lock, weather rating, scheduled codes
Typical price: $30–$80
See options on AmazonFrequently asked questions
Is a retrofit smart lock less secure?
It depends on your existing deadbolt, because the bolt and outside cylinder stay. If your deadbolt is solid, the retrofit adds smart control without changing the bolt.
Can I add a keypad to a retrofit lock?
Many retrofit locks pair with a wireless keypad accessory that mounts outside with adhesive or screws.
Does a full replacement need a new key?
Yes. The cylinder comes with its own keys, though some can be rekeyed to match your other locks.
Which is easier to install?
Retrofit is usually faster because only the interior part changes, but it needs clearance around the thumbturn.
Sources
- Allegion support — Understanding ANSI grades for locks
- Builders Hardware Manufacturers Association — ANSI/BHMA A156.36 Auxiliary Locks
- HUD and U.S. Department of Justice — Joint statement: reasonable modifications under the Fair Housing Act
- Seattle Police Department — Home security: door security
- Tucson Police Department — Neighborhood Watch home security booklet