Using location based reminders with Siri For iOS7
_Make sure Siri is activated
Settings >>> general >>>>> Siri >> TOGGLE Siri ON
Make sure location services is turned on and accessible by 'reminders'
Settings >>>> privacy >>> location services >>> TOGGLE ON >>>>
then scroll down to 'reminders' and TOGGLE ON
Make sure you have any locations you might use in your contact list along with the locations 'name'.
That should be it. You can then ask Siri to remind you to do whatever when you arrive or leave at a location. It's also really easy to ask Siri to remind you to do something at a particular time. For example, I might ask Siri to remind me to phone mum once a fortnight on Mondays at 9 in the morning.
It can take a little practice but I can nearly always to get it to work first time. I have set SIRI to give 'voice feedback' so I know if it doesn't understand
Settings >>> general >>> Siri >> voice feedback TOGGLE 'Always'
Incidentally, using location services does use more battery life.