Watch with built-in tag and method of determining authenticity of watch with built-in tag

A watch with a built-in tag for wirelessly communicating data, the watch comprising:

• a display configured to display a time;
• a metal case having a through-hole in a side surface;
• a metal crown disposed in the through-hole and configured to open and close the through-hole;
• and
• a wireless communication device housed inside the case,
• wherein the metal crown includes:
• a head disposed outside the metal case and that contacts the metal case to close the through-hole, and
• a shank extending from the head to the inside of the metal case through the through-hole with a first end connected to the head and a second end disposed inside the case, and
• wherein, when the head of the metal crown is pulled away from the metal case to open the through-hole, the head of the metal crown becomes contactless with the metal case and enables the wireless communication device housed inside the metal case to wirelessly transmit information to a reader device through the metal crown.