A deadbolt lock is a door lock with a solid metal bolt that extends into the door frame, operated by a key, thumbturn, or electronic actuator rather than a spring.
Most exterior doors use a deadbolt because of one crucial difference from a standard doorknob lock: it has no spring-loaded latch. The bolt stays “dead” until you turn the key, twist the thumbturn, or trigger the electronic actuator. That solid piece of metal reaches deeper into the strike plate, which makes forcing, picking, or manipulating it significantly harder than a standard spring latch.
How a Deadbolt Differs From a Spring Latch
A standard doorknob or lever lock uses a spring-loaded latch that retracts when you turn the handle. A deadbolt’s bolt does not move on its own. It only slides in or out when the control mechanism—key, thumbturn, or motor—actively moves it.
That difference matters for security. The solid bolt extends roughly one inch into the door frame’s strike plate, compared with the shorter spring latch that often sits closer to the edge. This deeper engagement makes it much harder to shim, kick, or pry open. Wikipedia’s entry on deadbolts notes this lack of spring action as the defining characteristic.
The Common Types of Deadbolts
Deadbolts come in three primary configurations, each with specific tradeoffs.
- Single-cylinder: Keyed on the exterior, thumbturn on the interior. This is the standard choice for residential front doors because you never need a key to exit quickly.
- Double-cylinder: Keyed on both sides. These offer extra resistance against someone breaking glass and reaching in, but they create a genuine safety hazard—if no key is available during a fire or emergency, you cannot get out. Schlage’s own guidance flags this egress concern plainly.
- Electronic/smart: Replaces the key with a keypad, fingerprint reader, or phone app, often paired with a mechanical deadbolt body. The security principle stays the same; only the actuator changes.
Single-cylinder designs dominate residential use for good reason: they combine solid security with safe, fast egress.
Key Specs to Check Before Buying
Deadbolts are not interchangeable. Fit depends on your door’s measurements, and mismatches are the most common cause of installation failure.
The critical numbers are the backset (distance from the door edge to the center of the bore hole), door thickness, and the bore hole diameter. Schlage’s B60 Series, for example, requires a door thickness of 1-3/8 to 1-3/4 inches and a bore hole diameter of 2.13 inches. The August Wi-Fi Smart Lock’s bundled deadbolt specifies a backset of either 2-3/8 or 2-3/4 inches, a 2-1/8-inch face bore, and a 1-inch edge bore.
| Specification | Typical Requirement | Why It Matters |
|---|---|---|
| Backset | 2-3/8 in or 2-3/4 in | Wrong backset means the bolt won’t reach the strike plate |
| Door thickness | 1-3/8 in to 1-3/4 in | Cylinder and thumbturn threads must match the door depth |
| Bore hole diameter | 2-1/8 in (face), 1 in (edge) | Deadbolt body must seat flush in the drilled hole |
| Bolt throw | 1 in standard | Deeper throw means harder to force |
| Handing | Reversible or non-reversible | Some models are handed; installing them wrong breaks function |
You should also look at the ANSI/BHMA grade. Grade 1 is the strongest, typically used on commercial doors; Grade 2 suits heavy-duty residential and light commercial use; Grade 3 meets basic residential standards. The August deadbolt, for instance, is rated Grade 3 under ANSI/BHMA A156.36. For premium security, some manufacturers offer Grade 1 options—Schlage’s L Series mortise deadbolts carry that rating, with a 1-inch throw and stainless steel bolt.
If you are already weighing an electronic upgrade, our roundup of the best bluetooth deadbolt locks covers models that keep these same mechanical standards while adding keyless convenience.
Deadbolt Grades and What They Mean
You will see Grade 1, Grade 2, and Grade 3 on most product pages. These grades come from ANSI/BHMA testing, which measures resistance to forced entry, cycle life, and security of the locking mechanism.
Grade 1 offers the highest level of residential and commercial security. Grade 2 is a solid, slightly more affordable middle ground. Grade 3 meets basic standards and is common in single-family homes. For most front doors, a Grade 2 or Grade 3 deadbolt provides reasonable protection; choose Grade 1 if you live in an area with higher crime rates or want maximum resistance.
FAQs
Can a deadbolt be picked easily?
All mechanical locks can be picked in principle, but deadbolts are harder than spring latches because the bolt’s movement is not aided by spring pressure. The lock cylinder still contains pins that must be aligned, so a skilled locksmith can pick one, but the extra effort relative to a knob lock is significant.
Is a double-cylinder deadbolt worth the safety risk?
Double-cylinder deadbolts resist break-ins through adjacent glass but require a key to exit from inside. Building codes in many jurisdictions restrict them on residential egress doors for this reason. If you choose one, keep a key near the door but out of reach of the glass.
Do I need a deadbolt on an interior door?
Generally no. Interior doors rely on privacy latches or simple knobs. Deadbolts are designed for exterior doors where forced entry is a concern, or for rooms containing valuable items or sensitive areas. A deadbolt on an interior door adds annoyance without much security benefit.
References & Sources
- Wikipedia. “Deadbolt.” Explains the defining lack of spring action and general deadbolt operation.
- Schlage. “Deadbolt Lock Guide.” Details on types, security benefits, and selection considerations.
- Schlage Commercial. “L Series Grade 1 Mortise Deadbolts.” Provides Grade 1 specifications including bolt throw and door thickness.