Indeed.
"It's called 'pay it forward' or Karma. Same thing.
A good way to do it is if you have something to give, post it and give a time limit, usually 5 days or a week, for people to say "I'm in!". Then draw a name. (Or put all the names on 'post-its' on a target, First one hit gets it.) That way it's fair for everyone involved, not just the first person who has a FREE alarm. And it makes it more interesting.
Usually the winner offers something else up, hence paying it forward, or passing on the Karma."