Bedroom door locks lock the door from the inside of the room. These locks are designed for privacy and not for security.
Generally, interior doors have a thumb lock. Since these doors don't have a key, the exterior of the lock can have a small hole that allows you to unlock the door with a long, thin piece of metal.
The outside of the lock can also have a release that can be turned with a coin, which will unlock the door from the outside.
For bedrooms you can also add a surface bold on the interior of the door. The bolt slides into a holder on the door frame. The door cannot be unlocked from the outside. This allows for more privacy.
There are many different interior door locks. The come in various styles and finishes. The interior door can have a key lock, but if you lose the key you cannot unlock the door from the outside.
Another style is the bed & bath knob. This lock has a standard locking procedure inside the room and a small hole on the outside. There are special tools available to unlock the door from the outside. You can also use a wire paperclip to unlock the door.
Average price for a standard interior lock is about $30.