Home Security Radar

What Happens When a Smart Lock Battery Dies? By Brand

When a smart lock battery dies, the lock stops responding to the keypad, app and auto-lock, but none of the makers covered here describes it unlocking itself (Kwikset says its locks stay in their last state). You get in one of three ways: the physical key (most keyed and retrofit locks), a 9V battery held to emergency terminals (key-free Yale, Schlage Touch, Kwikset Obsidian), or a USB-C power bank (eufy C220).

Figures researched 2026-10-01; each source below carries its access date. Prices change; treat any price here as "as of" its date.

How do you open a smart lock with a dead battery, by brand?

This is what each maker publishes in its manuals and support pages, as of October 2026:

LockBatteriesPublished battery lifeIf the battery dies
August Wi-Fi Smart Lock2 CR123A lithiumUp to 3 months with Wi-Fi onRetrofit over your deadbolt; your existing keys still work
SimpliSafe Smart Lock4 AANot published; several weeks of low-battery warningsUnlock manually with your key
Level Bolt, Level Lock1 CR2 lithiumUp to a year (Level Lock+ up to six months)Use the conventional keys that came with the lock
Yale Assure Lock 2, keyed models4 AA alkalineEstimated in the appUse your physical key; 9V emergency power is not available on keyed models
Yale Assure Lock 2, key-free models4 AA alkalineEstimated in the appHold a 9V battery to the terminals on the bottom of the lock, then enter your code
Schlage Touch Keyless Deadbolt1 9VNot publishedHold a new 9V battery to the contacts below the touchscreen, enter your code, then swap it in
Schlage Encode Plus4 AAUp to six monthsOne physical backup key is included
Kwikset Obsidian (keyless)Not stated on the backup pageNot statedTouch a 9V battery to the outside terminals under the touchscreen, enter a code, wait for the bolt to retract
eufy Smart Lock C2208 AAUp to four monthsPlug a power bank into the USB-C port on the bottom of the front lock, or use the key
Abode Lock4000mAh USB-C rechargeableUp to 12 months per chargeNot stated on the product page; it mounts over your existing deadbolt

The pattern is simple. If the lock has a keyway, the key is the fallback, and makers like Yale say so explicitly: 9V emergency power is only for models with no keyway. If the lock has no keyway, it has an external power trick, a 9V terminal or a USB-C port, and you need to carry or stash that battery or power bank somewhere outside the house.

None of the 9V or USB-C methods charge the lock. Yale says the 9V only provides temporary power to unlock and replace the AA batteries.

What warnings do you get before the battery runs out?

These makers publish low-battery warnings, so on their locks a lockout usually means a warning was missed.

  • SimpliSafe says the Smart Lock gives low-battery warnings for several weeks before it loses power: a slow blinking light on the lock, a message on the SimpliSafe Keypad and, depending on your settings, an app notification.
  • Yale reports four states in the Yale Access app: Sufficient, Low, Critically Low and Unknown. At Critically Low, Yale says the lock may stop responding at any moment. Notifications go out at Low and Critically Low.
  • Level shows "Replace Battery" at about 20% and "Battery Depleted" below about 10%. At Battery Depleted, motorized locking may fail but the key still works.
  • August sends an app notification and then an email when batteries need replacing.
  • Schlage Encode shows a flashing red battery icon when low and a solid red icon when the batteries need replacing immediately.

Two details change how reliable those warnings are. Level and Yale both say a Bluetooth-only lock only refreshes its battery reading when you are near it with the app open, or when it is paired to a Wi-Fi bridge. And Yale says turning the thumb turn by hand does not always send a battery update. If you never use the app, check the lock's own indicator now and then.

Battery chemistry matters too. Yale says its Assure 2 locks should use AA alkaline cells and not rechargeable, lithium or zinc-carbon ones, because the wrong type throws off battery reporting. August recommends CR123A lithium cells and not rechargeables. Level says never to use a rechargeable CR2, which can damage the lock.

Does a smart lock work during a power outage?

Yes, for every lock covered here, because they all run on their own batteries. Schlage states it directly: its smart locks are battery operated, so they keep working during a power outage. What an outage can take down is the remote side: Wi-Fi locks lose app control and notifications if the router is off, and locks that report through a Wi-Fi bridge or an alarm base station depend on that device's backup power. Our home security during a power outage guide covers how alarm systems and cameras handle it.

A few habits cover nearly every dead-battery scenario:

  1. Keep the physical key, if your lock has one, somewhere you can reach from outside, not on the kitchen counter.
  2. If your lock has no keyway, keep a 9V battery or a charged power bank in the car or with a neighbor.
  3. Replace batteries at the first low warning, with the chemistry the maker specifies.
  4. Fix a sticking deadbolt. Level says friction between bolt and strike plate makes the motor work harder and cuts battery life.

If you are choosing a lock, the dead-battery question favors keyed and retrofit designs, which keep a mechanical way in. That matters most for renters, where the retrofit models also keep the landlord's key working; see smart locks for renters. For the security trade-offs of key-free locks, see are smart locks safe, and for locks that tie into an alarm system, smart locks for security systems.

Frequently asked questions

Will a smart lock unlock itself when the battery dies?
No. We found no maker covered here describing a lock that unlocks when power runs out. Kwikset says its Aura lock stays in its last known state when the batteries are exhausted. The bolt stays where it was until you use the key or emergency power.
Where are the 9V terminals on a smart lock?
On key-free models they sit on the outside. Yale puts them on the bottom of the lock, Schlage Touch below the touchscreen, and Kwikset Obsidian underneath the touchscreen. Hold the 9V against them, enter your code, and replace the main batteries once inside.
How long do smart lock batteries last?
Published figures range widely: up to 3 months for the August Wi-Fi Smart Lock with Wi-Fi on, up to four months for the eufy C220, up to six months for the Schlage Encode Plus and Level Lock+, and up to a year for the Level Bolt. Wi-Fi, door friction and cold weather shorten it.
Can I use rechargeable batteries in a smart lock?
Most makers covered here say no. Yale recommends AA alkaline only, August recommends CR123A lithium and not rechargeables, and Level says a rechargeable CR2 can damage the lock. Abode is the exception, because its lock has a built-in USB-C rechargeable battery.

Sources

  1. August Wi-Fi Smart Lock: two 3V CR123 or CR123A lithium batteries; rechargeables not recommended; up to 3 months with Wi-Fi enabled; app notification then email when batteries need replacing: https://support.august.com/august-wi-fi-smart-lock-faq-rk6RzQ5YI (accessed 2026-10-01)
  2. August Wi-Fi Smart Lock attaches to existing deadbolt; existing keys still work: https://august.com/products/august-wifi-smart-lock (accessed 2026-10-01)
  3. SimpliSafe Smart Lock: 4 AA batteries; low-battery warnings for several weeks; slow blinking light, Keypad message, app notification; unlock manually with key if power lost: https://simplisafe.com/smart-lock-series-2 (accessed 2026-10-01)
  4. Level: CR2 lithium battery; Replace Battery at about 20%, Battery Depleted under about 10%; key still works; Level Bolt and Level Lock up to a year, Level Lock+ up to six months; do not use rechargeable CR2; friction reduces battery life; Bluetooth-only battery readings refresh when in range or with Level Connect: https://level.co/support/articles/level-locks-battery-guide/ (accessed 2026-10-01)
  5. Yale Access Battery Insights: Sufficient, Low, Critically Low, Unknown states; notifications at Low and Critically Low; 4 AA alkaline; avoid rechargeable, lithium, zinc-carbon; 9V emergency power on key-free models only via terminals on bottom of lock; keyed models use physical key; 9V does not charge the lock; manual thumbturn use does not always send battery update: https://support.shopyalehome.com/en_us/yale-access-battery-insights-ByM8Kgzg (accessed 2026-10-01)
  6. Schlage Touch: dead battery emergency jump start with new 9V battery on contacts below touchscreen, enter code, replace with the new 9V; battery-operated Schlage locks keep working in a power outage: https://www.schlage.com/content/dam/sch-us/documents/pdf/schlage-touch-deadbolt-home-sharing-tip-sheet.pdf (accessed 2026-10-01)
  7. Schlage Touch Keyless Deadbolt uses 1 9V battery with jumpstart feature; cylinder-free design: https://www.schlage.com/en/home/products/BE375CENFFF.html (accessed 2026-10-01)
  8. Schlage Encode: flashing red battery icon means low, solid red means replace immediately; all Schlage smart locks battery operated and continue to work during a power outage: https://www.schlage.com/content/dam/sch-us/documents/pdf/schlage-encode-deadbolt-home-sharing-tip-sheet.pdf (accessed 2026-10-01)
  9. Schlage Encode Plus: four AA batteries, up to six months of battery life with typical use, one physical backup key included: https://www.schlage.com/en/home/products/BE499WBCAMFFF.html (accessed 2026-10-01)
  10. Kwikset Obsidian 9V battery terminals underneath the touchscreen for dead internal batteries; Aura remains in last known state when batteries are exhausted: https://www.kwikset.com/support/topics/backup-power (accessed 2026-10-01)
  11. eufy Smart Lock C220: 8 AA batteries; up to four months; emergency unlock via USB-C port at the bottom of the front lock with a power bank; keyhole for physical key: https://service.eufy.com/article-description/Introducing-the-eufy-Smart-Lock-C220 (accessed 2026-10-01)
  12. Abode Lock: 4000mAh USB-C rechargeable battery, up to 12 months; installs over existing deadbolt: https://goabode.com/product/abode-lock/ (accessed 2026-10-01)

Related guides