1. www.electronics.howstuffworks.com/nfc-tag1.
2. blog.gsmarena.com/unlock-digital-tattoo/.
3. www.consumerreports.org.
4. www.gigaom.com/2013/08/16/why-youll-want-a-motorola-skip-to-securely-unlock-your-moto-x/.
5. en.wikipedia.org/wiki/Near_field_communication.