Also called cock cage, it is a device worn around the shaft and head of the penis - held securely in place with a testicule ring or a waist harness. Once the chastity device is locked, any form of erection become uncomfortable or impossible - preventing masturabtion & penetration.

Just slide your flaccid penis into the chastity cage that’s right for you, lock it up, hand over the key to the key holder, and you’re ready for a lifetime of torturous, denial-filled fun! Source: Wikipedia

Most of the time considered as a bdsm sex toy, people using chastity devices are looking for some kind of power exchange aspect. The wearer - also called the submissive - is giving up his sexual life to the whoever is holding the key - also called the dominant. However, it can be also used to prevent addictions such as masturbation or sex, by helping the wearer to control his pulsions and desires.

Some reasons on why people decide to lock it up:

For short sex play, tease and denial aspect is popular amongst chastity belt wearers. The tension increases knowing that there is nothing you can do until the keyholder decide on when to open the cage. Every little tease becomes intense arousal. Teasing is just as important as denial. they go hand in hand.With a penis cage on, you are forced to savor the moment rather than racing to orgasm like most of us do.

Caged up, you will be happy with any sort of release / stimulation, you could get. A simple lick by your Dom is a gift you must be thankful for. Also, the release after a long term wear is gratified with a more intense orgasm. Deprived from regular masturbation, your penis will become more sensitive and his orgasms will become stronger. Source: malechastitylifestyle

“My wife tells her friend that I am hung like a 7th grader.She has found a very good solution which is a nice young boyfriend, a great guy, that provides for her with what I lack. It works well and everyone is very happy, especially her which is the main thing.It took many years of encouragement to get her try it with another guy. We found a very nice man, well equipped and it went very well, better than I could have hoped for. I am happily now her cuckold husband for about 3yrs. She has had a few lovers but one that has been steady and has become a good friend. She is naturally dominating and I am submissive. We both really enjoy the lifestyle and she is very happy and much more satisfied and so am I. She found that she enjoys it much more than she ever thought she would, and I get a lot of pleasure from her key holding and control over me, tease and denial, having her lover over to our house whenever she wants.Being caged while serving and pleasuring my wife is unexpectedly more exciting and fulfilling for me than I ever expected and she is finding that my attention to her and her pleasures has been taken to a new level as well. A true win-win. The way things are going I am not sure she will ever unlock me, and at this point I am totally ok with it. :)”