Owning a breathalyzer of your own probably wouldn't be on the top of your priority list. A lot of us are very trusting of ourselves. We have high beliefs that "I'll be fine" and "I've done this type of thing many times before." I have a breathalyzer of my own and I have found a handful of reasons of why I'll keep it around. Here they are:
1) Keeping Yourself Honest
What is it about alcohol that gives you this blooming sense of confidence? I've walked out of many parties and bars completely convinced that I was perfectly fine to drive. It was only when I was on the road that I started second guessing myself. I'm assuming many people run into this as well. A breathalyzer can keep you honest. It'll help to remind your brain that you aren't as good as you think you are. To me, actually seeing the result and my BAC is very powerful to me because it's shown right there to me in black and white. No grey areas, you're either over the limit or you're not.
2) A Good Reminder
I put my breathalyzer in my car where I know I'll always see it. This way, I can remind myself to use it if I need to. For some, this won't work out so well. You might need to actually attach it to your keychain, if you can. Now, keep in mind that you could get busted for jumping into your car without the engine being turned on. Where I live, if you have the keys in the ignition, even if the car is off, you're subject to getting a DUI.
3) Save Your Life... And Others
Driving intoxicated is downright irresponsible. You know it. We all know it. No one needs to tell you. The problem is that we are always a little bit more inebriated than we really think we are. It's better to not trust yourself in these situations. I'm sure there are many people that love you. Take yourself out of dangers way and remove the possibility of hurting others.
4) Use It At Parties Or Social Gatherings
This could be a cool entertainment idea at parties. Now, don't drink so much that you're just trying to top the high score, that would defeat the purpose. People can easily make a huge game out of a breathalyzer, that's not what you want. However, as a designated driver, you could use it to monitor the BAC of others to ensure that people who are too drunk to drive stay safe. You can buy mouth pieces separately for pretty cheap. That way, things stay sanitary.
As an extra tip, I taped a piece of paper to the back of my breathalyzer with taxi cab phone numbers and the numbers of trusted friends that I could call should I ever need their help. This will take the work out of hunting for the information you need since you're less likely to do it when you don't have the information ready.