By Colin FosterWhen upgrading to a smart lock, you face two separate choices: retrofit or replacement hardware, and keypad or app-only operation. The first decision affects installation complexity, whether you keep your existing keys, and how the lock looks. The second determines how you and your guests enter—by typing a code, tapping a phone, or using voice commands. This article compares both dimensions so you can pick the right combination for your door.
Understanding Retrofit and Replacement Smart Locks
How Retrofit Smart Locks Work
A retrofit smart lock replaces only the interior thumb turn of your existing deadbolt. The exterior keyed cylinder and the bolt mechanism stay in place. The new interior component contains the motor, battery pack, and wireless radio. You install it by removing the old interior escutcheon and attaching the retrofit unit. Because you keep the original deadbolt and key cylinder, your existing keys still work on the outside. The retrofit adds motorized turning—so you can lock and unlock from your phone, by voice, or on a schedule—while retaining the manual key option.
How Replacement Smart Locks Work
A replacement smart lock swaps out the entire deadbolt assembly, including the exterior keyed cylinder. The new lock often comes with a keypad on the outside (or a fingerprint reader, or both) and a sleek interior assembly. Installation is more involved: you remove the old deadbolt, install the new latch and strike plate, mount the exterior keypad, and connect the interior and exterior components with a cable that runs through the door. Some replacement models can be rekeyed to match your existing house key; others come with a set of new keys. Some models offer a key override; others rely entirely on keypad or app access.
Keypad vs App-Only Control
Keypad Smart Locks
Keypad locks have a numeric or touchscreen interface on the exterior. You assign a unique code to each person. Guests enter the code to unlock the door without needing a phone or app. Codes can be temporary (for a service worker) or permanent (for family). The lock works even if your phone battery dies because the keypad draws power from the lock’s own batteries. The downside: you must manage codes—creating, modifying, and deleting them—through the lock’s app. Also, the keypad adds a physical element that some find less sleek.
App-Only Smart Locks
App-only locks lack an exterior keypad. You unlock using your smartphone via Bluetooth, Wi-Fi, or a voice assistant. Many include geofencing (auto-unlock when you arrive) or touch-to-open sensors. Some app-only models add a fingerprint reader as a backup, but pure app-only units offer no code entry at the door. The major drawback is phone battery dependency. If your phone dies or you misplace it, you are locked out unless you carry a backup key (some models include a physical key override). Guest access requires you to send a digital key through the app, which can be convenient for managing access remotely but less intuitive than handing out a code.
Side-by-Side Comparisons
Retrofit vs Replacement Smart Locks
| Feature | Retrofit Lock | Replacement Lock |
|---|---|---|
| Installation difficulty | Low – swap interior plate only | Moderate – full deadbolt replacement |
| Keeps existing keys | Yes – original key cylinder stays | No – new keys or rekeying required |
| Renter-friendly | Yes – easy to revert; no permanent change to door | May need landlord permission; more permanent |
| Appearance | Bulkier interior with protruding motor housing | Streamlined, integrated design |
| Guest access codes | Available only if model includes exterior keypad | Often built into exterior keypad |
| Fingerprint option | Rare on retrofit models | Common on replacement models |
| Wireless protocol | Usually Wi-Fi or Bluetooth; some support Thread | Wider range: Wi-Fi, Bluetooth, Zigbee, Z‑Wave, Thread |
| Security considerations | Physical lock is original (keyed); motor may be vulnerable if interior is exposed | Integrated design can include tamper alerts and encrypted communication |
Keypad vs App-Only Control
| Feature | Keypad Lock | App-Only Lock |
|---|---|---|
| Entry without phone | Yes – type a code | No; may have fingerprint backup |
| Guest access | Simple – share a code | Must send digital key via app |
| Phone battery dependency | Low – lock works independently | High – dead phone means lockout |
| Exterior appearance | Numbers/touchpad visible | Minimal; often just a sensor or fingerprint pad |
| Auto-unlock (geofencing) | Often supported via app | Common feature |
| Battery life of lock | Lower due to keypad backlight | Usually longer; no display |
When a Retrofit Lock Is the Better Choice
Retrofit locks shine for renters. Because you do not replace the cylinder or the bolt, you can take the smart module with you when you move and reinstall the original thumb turn. No permanent alteration to the door means you avoid risking your security deposit. If you already have a high‑quality deadbolt that you trust, a retrofit gives you smart features without compromising the physical lock. Installation takes around fifteen minutes and requires only a screwdriver. Retrofit models are also a good fit if your door has a non‑standard bore or size, since you keep the existing hardware.
However, a retrofit lock adds bulk to the interior side. The motor housing can protrude noticeably, which may interfere with a storm door or nearby furniture. Physical security stays the same as your existing deadbolt. If you want fingerprint entry or a fully flush appearance, a retrofit probably won’t satisfy those needs.
When a Replacement Lock Is the Better Choice
Choose a replacement lock if you own your home and want a polished, integrated look. Replacement models let you pick from a wide range of finishes, keypad or touchscreen styles, and biometric options like fingerprint readers. They often support more wireless protocols—Zigbee, Z‑Wave, or Thread—making them easier to integrate with a full smart home system. If you want to give guests, house sitters, or cleaners temporary codes that you can manage remotely, a replacement keypad lock is the most straightforward solution.
Replacement locks can also include features such as tamper alerts because the entire assembly is designed as one unit. Some models include a hidden key slot; others rely entirely on electronics. If you prefer a smart lock that works with your existing smart home hub or voice assistant, check the compatibility notes on the product page. For more on how different locks compare across brands and protocols, see our Smart Lock Comparisons page.
Keypad vs App-Only: Which Control Method Suits You?
When Keypad Is Better
If you frequently have visitors who need access—dog walkers, house cleaners, family coming by—a keypad lock eliminates the need to hand over a physical key. You assign a temporary code that expires, and you don’t have to worry about your phone battery. Keypad locks are also more practical for households where multiple people come and go at different times. Everyone can have their own code, making it easy to track who entered (the app logs each access). For elderly family members or guests who aren’t comfortable with smartphone apps, typing a code is far more intuitive than downloading an app and accepting a digital key.
When App-Only Is Better
App-only locks appeal if you prioritize a minimalist exterior and prefer hands‑free entry. Many can be set to auto‑unlock when your phone approaches, so you never need to type anything. The lack of a keypad also means one less surface for weather and grime. If you live alone or with one other person and you always carry your phone, the convenience of geofencing may outweigh the risk of a dead phone. Some app-only models offer a fingerprint reader as a backup, which solves the battery‑failure problem without adding a keypad. But in a pure app-only lock with no secondary entry method, you need to keep a physical key hidden somewhere or give a trusted neighbor a spare.
Upkeep and Long-Term Ownership
Both retrofit and replacement locks run on batteries (often AA cells; check the model). Battery life varies widely but expect to replace them every few months to a year, depending on usage, keypad backlight frequency, and wireless connectivity. Some smart locks send a low‑battery alert to your phone; others blink the keypad or sound a beep. Always replace batteries promptly to avoid being locked out. Many models still allow manual key operation even when the battery is dead, but pure app-only locks without a keyhole become unusable—carry the physical key or a portable battery pack if your model supports emergency power via USB.
Firmware updates are important for security. Most smart locks check for updates through their companion app. Keep the app updated and apply firmware as soon as it’s available. Over‑the‑air updates patch vulnerabilities and sometimes add features (like new codes or integrations). Pay attention to wireless protocol compatibility. If you plan to use Matter or Thread, verify that your lock and your smart home hub support the standard. For more on wireless standards for smart devices, see our Wi‑Fi vs Zigbee vs Thread Smart Bulbs guide—the same concepts apply to locks.
Physical security is still paramount. A smart lock is only as strong as the door and the deadbolt mechanism. Make sure the strike plate uses long screws into the door frame, and consider a reinforcement kit if your door is weak. Retrofit locks inherit the security of your existing deadbolt, which may be a lower grade—upgrade the deadbolt itself before adding a retrofit if needed. For replacement locks, check the ANSI/BHMA grade listed by the manufacturer; Grade 1 is the highest residential rating.
FAQ
Can I use a retrofit lock with a smart home system?
Yes, many retrofit locks connect to Wi‑Fi or Bluetooth and work with major smart home platforms. Check the product specifications for compatibility with your preferred voice assistant or smart hub. Some retrofit models also support Zigbee or Thread, which may require a compatible hub.
Do app-only locks have a backup entry method?
Some do, some don’t. A few app-only models include a hidden keyhole or a fingerprint sensor. Others rely entirely on the phone or a voice assistant. Read the manufacturer’s description to confirm whether a physical key override is available. If it’s not, plan for a backup: a spare battery pack that can power the lock via USB, or a key hidden in a secure lockbox.
Are smart locks secure?
Reputable smart locks use encrypted wireless communication, but no lock is invulnerable. Check the ANSI/BHMA grade of the deadbolt, keep the firmware updated, use strong unique codes, and follow the installation instructions carefully, including long strike-plate screws. For a deeper look at how different locks compare, visit our Smart Home Comparisons page.
Can renters install a smart lock?
Retrofit locks are the safest option for renters because they don’t alter the door’s permanent hardware. Always check your lease agreement first. Many landlords allow retrofit installations as long as you can restore the original thumb turn when you move out. Replacement locks typically require drilling new holes or changing the cylinder, which needs written permission from the landlord.
Choosing between retrofit and replacement is mostly about installation commitment and design preference. Choosing between keypad and app-only is about how you and your guests want to enter. Many smart locks combine a keypad with an app, offering the best of both worlds. Decide which trade‑offs matter most to you—rental flexibility, code sharing, phone reliance, or appearance—and you will find the right option for your door.
About Colin Foster
Colin Foster is part of our editorial team and reviews and edits our smart home guides, checking product details against manufacturer specifications and owner feedback.
