One Sided Deadbolt: No-Key Locks for Inside Security

Locks that can be picked or bumped all have one thing in common: a keyway on the outside. A one sided deadbolt removes it. The inside has a normal thumb turn, and the outside shows only a smooth blank plate, so there is nothing for a burglar to pick, bump or drill from the exterior. It is a smart extra layer for a back door, a basement or garage entry, an apartment door at night, or a door that only family members use from the inside.

There is one big limitation. Because it cannot be locked or unlocked from outside, a one sided deadbolt cannot be the only lock on the door you use to leave the house. You need a keyed lock on at least one exterior door so you can lock up behind you and get back in.

What Is a One Sided Deadbolt?

Also called a single sided deadbolt, one way deadbolt or blank-plate deadbolt, it is a standard deadbolt body with a thumb turn on the inside and a cover plate on the outside. Turning the thumb turn throws a hardened bolt, usually 1 inch long, into the door frame. The bolt cannot be pushed back in by force against its tip, which is what makes any deadbolt stronger than a spring latch.

Compare it with the other common styles:

• Single cylinder deadbolt: key outside, thumb turn inside. The standard front door lock.
• Double cylinder deadbolt: key on both sides. Harder to escape through in an emergency, and restricted by many local codes in homes.
• One sided deadbolt lock: thumb turn inside, nothing outside. Only works when someone is inside.

Where a Single Sided Deadbolt Makes Sense

The best uses share one trait: the door is locked from inside while people are home, or it is never used to come in from outside.

• Secondary exterior doors. Back doors, side doors and basement walkouts that are always exited through the main door.
• Doors from the garage into the house. If the garage door has its own lock, an extra blank-plate deadbolt stops someone who gets into the garage.
• Apartment and condo doors. Adds a nighttime lock that a master key or a copied key cannot open from the hallway.
• Bedroom or home office doors. Privacy and security inside the home, with easy escape from the inside.
• Double doors and French doors. On the inactive leaf, a second lock helps hold it closed.

Renters should check their lease and local rules first. Many landlords require access for maintenance and emergencies, and some leases restrict extra locks or require a key copy for added hardware. Get written permission before drilling.

Why It Cannot Be Your Only Exterior Lock

The obvious problem is practical: the last person out of the house cannot lock it. The less obvious one is emergency access. If someone inside falls ill while the blank-plate bolt is thrown, family members and emergency responders cannot unlock it from outside and may have to force the door. Keep that in mind for households with older relatives or someone with a medical condition.

On the plus side, a thumb turn is a single motion to unlock from inside, which keeps fire escape simple. That is a key advantage over a double cylinder lock, where a missing key during a fire can trap people.

Tools and Materials

• One sided deadbolt kit (bolt, inside thumb turn assembly, outside blank plate, strike, screws)
• Drill with a 2-1/8 inch hole saw and a 1 inch spade or auger bit (only for new installs)
• Door lock installation jig (optional but helpful)
• Chisel and hammer for mortising the bolt faceplate and strike
• Tape measure, pencil, screwdriver
• 3 inch wood screws for the strike plate

How to Install a One Sided Deadbolt

Many kits are designed to fit a standard deadbolt prep. If the door already has a deadbolt hole, installation takes about 20 to 30 minutes. A new installation takes about an hour.

1. Pick the height. On a door with an existing knob, place the deadbolt about 5 to 6 inches above it. For a stand-alone bolt, pick a comfortable reach height.
2. Mark with the template. Tape the paper template to the door edge and face. Set the backset (2-3/8 or 2-3/4 inches) to match the bolt.
3. Bore the face hole. Drill the 2-1/8 inch cross bore from both sides, stopping when the pilot bit pokes through, so the veneer does not tear out.
4. Bore the edge hole. Drill the 1 inch edge bore straight into the cross bore.
5. Mortise the faceplate. Trace the bolt faceplate and chisel a shallow recess so it sits flush with the door edge.
6. Install the bolt. Insert it with the correct side facing up (most are marked “up”), then screw it in place.
7. Mount the blank plate and thumb turn. The outside blank plate goes on the exterior face; the inside thumb turn assembly engages the bolt tailpiece. Tighten through-bolts evenly.
8. Mark and install the strike. Throw the bolt against the frame to mark its center, drill a 1 inch hole about 1-1/8 inches deep, then mortise and install the strike with 3 inch screws into the framing.
9. Test it. The bolt should throw fully with the door closed, with no binding.

Using a blank plate instead of a cylinder means there is no need to coordinate keys with other locks in the house.

Strengthening the Door Around the Lock

Any deadbolt is only as strong as the frame it locks into. Most forced entries split the jamb rather than defeating the bolt. Upgrade with a reinforced strike plate, long screws into the framing, and a door edge guard if the door is wood. A solid-core or metal door also matters: a hollow-core interior-grade door can be kicked through regardless of the lock.

Hinges deserve attention too. On an outswing door with exposed hinge pins, add security studs or non-removable pins so the door cannot be lifted out of the frame while the bolt is still thrown. Swapping one short screw in each hinge leaf for a 3 inch screw that reaches the stud also stiffens the whole hinge side, which helps the door resist kicks on both edges, not just at the lock.

Look for an ANSI/BHMA Grade 1 or Grade 2 rating on the deadbolt itself. These grades test bolt strength, cycle life and resistance to force.

Troubleshooting

The bolt does not fully extend. The strike hole may be too shallow or misaligned. Deepen it to at least 1 inch and check alignment with a crayon mark on the bolt tip.

The thumb turn is stiff. Loosen the through-bolts slightly. Overtightening squeezes the mechanism. If it is still stiff, the tailpiece may be cut too long for the door thickness.

The blank plate feels loose. Some plates secure only with the through-bolts from the inside. Tighten evenly and check that the plate sits flat on the door.

The door rattles when locked. Adjust the strike position or add weatherstripping so the door seats snugly.

Cost Ranges

A residential one sided deadbolt usually costs about $20 to $80, with heavier commercial versions costing more. A reinforced strike kit adds a modest amount. A locksmith or handyman typically charges a moderate hourly or flat fee for installation, more if the door needs new bores or reinforcement.

When to Call a Pro

Call a locksmith for metal or fire-rated doors, doors with glass close to the lock area, or when the existing bores are damaged or out of alignment. A carpenter can repair a split jamb or reinforce the frame. Renters should get the landlord’s approval and may need the landlord’s locksmith to install the lock.