Putting a condom over your vibrator is a good way to extend its life and make clean up easier, but it isn't necessary for solo masturbation unless you're using the vibrator in both your vagina and anus. You should never put anything in your vagina after it's been in your rear, so if you're using your vibrator anally, cover it with a condom first, then remove the condom before you insert it in your vagina or touch it to your genitals.