A short aluminum alloy arm that screws to your door frame and swings across the door, so the door cannot open even when somebody on the other side has a key. It goes above the handle, which is what matters if there is a toddler in the house.
No keyway. No batteries. No app. Four screws into the frame and it is done.
A deadbolt keeps out strangers, and that is a different problem
You already know what the lock on your front door does. What it cannot do is tell you apart from everybody else holding a key, and once a house has been rented twice, sold once and had a spare cut for a neighbor, that list is longer than most people care to add up.
This one has no keyhole at all. Nothing on the outside of the door touches it. It is set by hand, from the inside, and while the arm is across the door it makes no difference what is turning in the deadbolt.
Small hands, and a lock they cannot work
Most people fit one of these the year their child learns to reach the handle. The mounting plate goes on the frame well above it, so the whole mechanism sits somewhere a toddler cannot reach.
Opening it is a two-finger job. You pinch the recesses at the top and bottom of the arm between a thumb and one finger, slide it across, then swing it clear of the door. Two movements, and you stop thinking about it after the first day. Pulling on it does nothing at all, which is the entire point.
Why a chain or a swing bar is not the same thing
A door chain and the little swing bar in hotel rooms both do the same trick: they let the door open a few inches and then stop it. That gap is their whole purpose, and it is also a gap: wide enough to put an arm through, and wide enough that the door is already moving before anything takes the strain.
This arm stands proud across the closed door's edge instead, so the door does not travel. The other half of the difference is where it is anchored. A chain usually goes into the casing on two short screws through soft trim. This plate takes four into the frame, three through round holes and the fourth through a horizontal slot, so you can line the arm up against your own door before you tighten anything.
What it needs from your door
One thing decides whether this works in your house. The door has to open inward, into the room you are standing in. Outward-opening doors are out, and so are double doors, slatted doors and a frame too wide for the arm to reach across. The full list is in the specifications below, and it is worth reading before you order.
Nothing is cut into the door itself. Four screws go into the frame with a 1/8 inch bit, and the day you move out the whole thing comes off and leaves four holes in the jamb. That is why so many end up on rented doors.
It sits folded flat against the frame all day, and takes a second to put across at night.
Specifications
Dimensions: 3 x 2.43 x 1.37 in (7.6 x 6.2 x 3.5 cm), height x depth x width
Arm: 3 in (7.6 cm) tall, 1.37 in (3.5 cm) wide, 1 in (2.5 cm) deep
Mounting plate: 2.18 in (5.5 cm) tall
Material: Aluminum alloy
Colors: Black, White and Silver, with the mounting plate finished to match the arm on all three
Fixings: Four screws per lock, included
Fixing holes: Three round holes and one horizontal slot for lining the arm up
Drill bit: 1/8 in
Operation: Swing arm on a vertical pivot. Pinch the recesses top and bottom, slide, then swing clear to release
Keys: None. There is no keyway, and nothing outside the door operates it
Fits: Doors that open inward, into the room
Will not fit: Doors that open outward, double doors, slatted doors, a door frame too wide for the arm to reach across, or a door seam narrower than 0.07 in
Quantity: One lock, or two
Package Includes
1x Door Lock, or 2x on the 2 Pieces option
4x Mounting Screws, or 8x on the 2 Pieces option