In an aspect, the present disclosure provides an electronic device for OTP authentication of a present location, comprising: a power source, a processor, and a memory in a housing; a strap comprising first and second ends, and a first wire extending from the first end to the second end of the strap and forming an external loop, wherein the first wire establishes a first electrical connection between the power source and the processor; and a second electrical connection operatively connected to the processor and the memory, the processor configured to generate an OTP, only when the processor is connected to the power source by the first electrical connection without interruption once the first electrical connection is established. The OTP authentication may be time-based one-time password (TOTP) authentication, and the generated OTP may be a time-based one-time password (TOTP).