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I'm writing a PHP-based API around some data that is updated as frequently as once a minute, or as infrequently as once every 15 minutes. I'd like to have a cron job push alerts to end users when certain criteria is met (e.g. data goes above a certain threshold), but because my data changes so rapidly and is prone to wild fluctuations, I'm not entirely sure how to approach this. For reference, users can include, for example, people who have downloaded my Pebble smartwatch app, or my upcoming mobile phone app. The data that I'm most interested in (which, if you're interested, is from the ACE spacecraft, and is used to help people view the northern or southern lights) changes every fifteen minutes, and the Kp index it provides is used as a (arguably) good indicator of how likely you are to see an aurora. Values under 5 are usually of no interest to most, anything above 5 (up to 9) are worth getting an alert about. These values can fluctuate, so if a Kp 5 storm is expected, it can hit 6, then dip to 4, then back to 5 and so forth. This is due to the particles ejected from the sun not being a nice, even "wave". I've personally witnessed nights where Kp goes up, then sits low for a while, so you head home, only to find that 10 minutes later it picked up again. Aaanyway, back to my story, I'd like to find a way to alert users about these values when they're of interest, but without bombarding them with notifications, or missing too many events. Here's the various options I've considered: Send an alert every 15 minutes (too often, too annoying, not 'smart') Send an alert every 15 minutes, but only if the value has increased, then "reset" the check after a period of time (better, but what if it hits 7, then dips to 4 for 45 minutes, then hits 6.99? You'd miss out on an alert!) Find a way to check if the user has dismissed the notification and don't re-send it to them for an hour (not feasible, as Pebble's UX doesn't really allow for that, not to mention iOS doesn't have a way to notify your app when an alert has been dismissed) Some kind of data check, where if a value has remained high for longer than 30 minutes, it's alert-worthy and one gets sent out (but you'd miss out on stuff if the value is high for 29 minutes)And riding on the back of that, if the value remains stable, prime the alert. If it increases after it's primed, send the message. I'm more than happy to do some reading and learning. I just didn't exactly know what to search for, as I'm not dealing with something like storage space (where you can send an email if it hits < 20%, and it's unlikely that the storage will fluctuate between 20% and 21%, causing repeated messages) or rare events like CPU usage that you can alert if it stays high for longer than x many minutes