Which most common devices people use to prevent falls?

Hipsaver is one.

There are pants that have padding on the hips which can help if a person does fall, and several companies make them, but I don't remember the name of the companies.

There are bed alarms that can alert you when someone gets up and similar devices for chairs, there are motion sensors or pressure sensitive mats that will alarm when people pass by. All of these can be helpful, but they can't completely stop the falls from happening.

If the caregiver is from an Agency, that caregiver has to be fully awake during her shift. My Dad has had night Agency caregivers and they were able to hear Dad put his feet on the floor and the caregiver would quickly go to his room to see if he needed any help.