For the door side screws with a length1 8 to1 4 shorter than the thickness of the doorwill give the most strength.
How to install a chain lock on metal door.
Install a deadbolt lock to a steel door with help from a home improveme.
Tape up the template for the lock plate.
The locks consist of two sides the secured side where the chain is firmly bolted and permanently set then the sliding side where the knob at the other end of the chain can be inserted and slid into place.
Also if possible use minimum 10 screws butit s always best to take the latch to the hardware store to get the correctscrew sizing.
Position it about 3 to 6 inches above the deadbolt on your door.
As da01 mentioned a good 12 volt drill should manage this just fine if you are using a drill bit designed for metal.
Move the fixed peg portion on the door face where the swinging arm easily.
Position the lock with the swinging arm portion on the door frame near the edge with the arm extending over the door.
This is the part that is not attached to the chain.
If you do not have a deadbolt on the door place it about three to six inches above the door handle.
I ve tried millions of things to get a hole in the steel door.
A door chain lock is an additional lock to the standard deadbolt and door handle locks that may already be on your door.