What you will need:

• An android based phone

• a RFID tag, which can be a card, fob or any other MiFare compatible card

• access to Google play store

Install the NFC Tools app from https://play.google.com/store/apps/details?id=com.wakdev.wdnfc&hl=nl&gl=US

Open the app and hold a RFID card to the back of your android phone.

a screen will appear with details of the card:

You will need the "Serial Number", note that this is in a hexadecimal format. You do not need to enter the ":" when using the serial number when entering it in the wattify platform. They will however automatically be removed when you would copy and paste them.

PS: This will currently NOT work on iOS, even if the NFC Tools app exists for iPhone and iPad.