Foursquare has just made it easier to keep track of your friends' check-ins, even if they aren't nearby. Now, you can
stalk keep tabs from a distance with the new "Always on" notification feature
"Have friends or family that live in another city, state, or country? Now you can choose to receive notifications when they check in, even if they’re not nearby or you have all check-in notifications turned off. Is your spouse traveling for work? See when he or she arrives at the airport safely. Friends visiting Iceland for a week? Easily keep up with their glacier-climbing, fermented-shark eating adventures," said the company in a blog post.
Note that enabling "always on" for a particular friend will override the fact that you've turned all notifications off.
All you have to do is go to a friend's profile and open up the drop-down menu at the top right. There, you'll find three options for when you'll receive their check-ins via notification: when they're nearby, never, and the new "always."