How to remember to switch off your NFC?
Use NFC Reminder !

Are you using NFC for contact-less paying with your mobile phone? Then you should better switch-off your NFC after paying to avoid draining your battery and to avoid the risk that someone gets in contact to your mobile phone from your pocket.
NFC Reminder helps you to remember do this as soon as possible.
Just enable NFC, make the payment, and after a specified time you will get a notification to switch off the NFC option.

NFC Reminder can not switch off NFC option on your phone due to Android regimentations. Only the user can enable/disable NFC. That's why NFC Reminder just creates a notification for you to remember to disable NFC.