Once a minute is fine, it is only checking the element. I haven't tested it but abc123 could verify if it is pulling all the js and images to have to check. If not then that's even better.
I like OMGsus he makes me happy. AlertBox at the very most is pulling down the html, this is all text it doesn't include any images. And at the very least is pulling down an html element. The store html page in total without images is 30.0KB, once it is all in it is 8.28KB.
This means let's say 2000 people follow this tutorial:
60000 + 977040 + 22852800 = 23889840 /1024 = 23329.921875MB a day
30.0(2000) + 8.28 (2000)(59) + 8.28 (2000)(60)(23)
It's either that or the F5 (Mozilla Auto-Refresh) method:
341(2000)(60)(24) / 1024 = 959062.5MB a day
This is completely ignoring caching, I am sure people will argue that people aren't all going to refresh every minute by hand and I agree, but let's also say this provides piece of mind, meaning it will hopefully calm some of the people who are ready to stab someone.
If you count caching and assume AlertBox only download the 15Bytes required for it to perform the real action necessary then it drops down to almost unnoticeable.
This also gives the advantage of email notification over no notification at all.
