Counting the time a user has been connected to a site

At the moment I'm using this SQL to check if a user is connected:

date_add(last_activity, INTERVAL 3 MINUTE) > NOW()

This is passive and will only trigger when a page is loaded.

What I'd like to do is a system that checks if a user has remained connected during a given span of t开发者_运维技巧ime and give them bonus points.

What do you suggest to achieve this? Use polling or another approach?

You need to use some kind of java script that will report activity using ajax to your site in intervals of like 1 min. You need to implement some sort of mechanism to check if user is active, like if the mouse moves or page is scrolled, because some users can use the same page for long times. If the page is not used since the last min(should be a global var in javascript, set to true every mouse move, and to false every time a message is sent) you don't send a message.
When you receive the ajax notifications in the server you check the time between the last ajax notification(should be stored in database) and current notification and if its smaller than an interval (maybe 2 mins) give the user points for it.

As said you can use AJAX and alternatively the Refresh META tag. Note that if I see a browser tab constantly refreshing, I close it as it is distracting. Of course, if you're offering a service that requires frequent refreshes (chat / shoutbox, ticker) then it's less disturbing.

I currently have 14 tabs open, some of which for days which I haven't really looked at, so you gotta ask how valuable your information is. As far as I know, javascript is unable to get the current mouse position if it's not moving over something that has the mousemove event handled, so implementing "is the page in view and the user moving her mouse" may prove to fire a lot of events when user is active.

I may be oversimplifying here, and this probably won't help much if you're trying to charge for time on the site or something like that, but this is something google analytics takes care of. Time on site is a metric they actively record.

Ok. So here is my idea. As I mentioned in comment my way would be javascript timeout and AJAX.
So the idea would be something like this:

1. Make a global variable for mouse position.
2. Set timeout for function to fire in around 10 second intervals (which can grow in time).
3. Function compares last mouse position with current mouse position. If it has changed user is presumably active.
4. Update global variable for mouse position. And send data to server-side.
5. Rinse and repeat...

Actually thing that changed can be anything if you want, but mouse position would be most suiting I think.