I once googled "what is the beeping noise in my house" as an act of sheer desperation. I'd spent hours trying to figure out what was making the noise after turning off every electronic thing I owned (and I own a lot of them!). Amazingly, I actually got the answer! It turns out that I had put my old smoke detector in the back of a closet and forgotten about it.

I was reminded of that again today, when both my dishwasher and dryer had been beeping for hours. Like my smoke detector, the sound is strident and impossible to ignore. However, unlike the dishwasher, the constant beeping is also completely unnecessary. Once it's beeped three times once, and maybe again an hour later, I really don't need to be constantly annoyed by the dishwasher letting me know that it's done. However, I do actually need to know that the smoke detector battery is dead.

Funnily enough, I was interrupted by the sounds as I was in the middle of working through our notification messaging, and thought it was a great lesson in the art of notification design. Broadly speaking, notifications fall into three categories:

informative - informing a person about an event he/she should be aware of
requestive - informing a person about an event that you want him/her to take action on
active - informing a person about an event he/she needs to take action on

I should also note that I'm defining notifications as broader than just in-app push notifications. A notification is anything that informs the user of an event, whether email, text, sound in a browser window or something else.

Here are some of the key things to consider for these different types of notifications:

Informative

e.g. a payment has been made successfully
be thoughtful about whether the user actually wants to know this information
the event should be something he/she cares about
when users don't need to take action, don't get in their face
define the headline (i.e. the minimum info they need to be aware of) v. the article (the additional data that is useful but is skimmable)
notify once, or maybe twice with the appropriate wait time in between notifications

Requestive

e.g. provide an app rating
what's important to you isn't necessarily important to your user
you're asking them to do you a favour
if you don't show that you're thoughtful about their time, you're more likely to lose their goodwill
as far as possible, allow the action to be taken within the notification, e.g. embedded form in an email
keep the request simple and easy, e.g. a 3 question survey instead of a 10 question survey
think about whether you can or should offer the user something in return for their work

Active

e.g. choose an account to make a payment
these often relate to payment, or something negative - how can you soften the blow?
copy is critical - show people you're respectful of their time, be factual and succinct
again, define headline v. article
include all the information they need to make the decision
provide confirmation that it's been done

So as you think about your product's notification strategy, consider the categories in which they fall, recognize that you're being interruptive and think about how to be respectful of your user's time.