A deadbolt is a great idea as an additional lock for a sliding glass door. It can be installed either on the top or the bottom of the door.
These locks are very practical and are among the best deadbolt options for sliding doors. There are different types—some use a simple hook, while others use a pin that goes inside the door, which requires drilling a hole. This older pin-style lock is not recommended and was commonly used many years ago.
The extra lock is mainly for added peace of mind and improved child safety. We know that if someone really wants to break the glass, even ten deadbolts won’t stop them—but having one extra lock is still a good safety measure.