Technology gives us a lot of tools to remind us in its time about something. Calendars, Alarms, Notebook apps etc. can do this.
Now we speak about reminder by locations. It is very useful tool which can remind us f.e. to buy something from gift shop when we are near. Or when we pasted half way, automatically send sms to our friend that i am arriving, half way pasted. So in such cases time is not important, but location is. I use two services for this purpose.