Installation of back up alarm

First: I am curious if a back up alarm is necessary. I do not intend to use in place of a person backing me up. Although, there may be instances that a backup person is not available and a backup alarm might be useful. If so, what would one recommend to be the best buy and quality to be installed. And how would one install it. I understand that there is one out there that can be plugged in where your backup light fits. Also, is a on/off switch necessary in the drivers area? I appreciate any and all comments.
Respectfully,

Ken