A Comparison of Self-Setting Clocks

What is the self-setting feature of a clock?

  • Ideally, it is the ability of a quartz clock 1) to automatically set the time correctly when it is first used, and 2) to keep accurate time over the course of its use. Other practical considerations include time zone, daylight saving time, power outage recovery, and connectivity requirements.

Types of self-setting clocks

Self-setting clocks can be based on different synchronization technologies.

  • ‘Atomic’ clocks (narrowly referring to consumer products called WWVB Radio Controlled Clocks)
  • GPS clocks
  • Wi-Fi clocks

atomic clock

gps clock

reason clock

Comparison of self-setting clocks

Atomic clocks

GPS clocks

Wi-Fi clocks

Source of the correct time

periodic sync signals from NIST radio station

GPS satellite signals (highly accurate time is a ‘by-product’ of GPS)

Requires Wi-Fi connectivity and communication with NTP time servers

Common functionality

Periodically synced with the correct UTC time

Device-dependent functionality

Correct for time zone and daylight saving time; power outage recovery

Coverage area

Most places in North America

Worldwide, wherever GPS covers

Worldwide, wherever there’s access to Wi-Fi and the Internet

Indoor signal strength

Depends on geographical location and which room 

Can be greatly affected by which room it is in

Only depends on the Wi-Fi signal strength and Internet connectivity

Speed of sync for the first time

Usually longer than 1 minute and can take up to 5 minutes

Depends on the TTFF of the GPS receiver in the clock. 2 to 4 minutes typical

Very fast. Less than a minute



  1. NTP - Network Time Protocol
  2. NIST - National Institute of Standards and Technology
  3. UTC - Coordinated Universal Time (that is, the time kept at the Prime Meridian that passes through Greenwich, England.)
  4. TTFF - Time to First Fix
  5. LF - Low Frequency


  1. https://www.nist.gov/pml/time-and-frequency-division/radio-stations/wwvb/help-wwvb-radio-controlled-clocks
  2. Reason ONE Smart Alarm Clock with Alexa Built-in for Smart Home
  3. https://en.wikipedia.org/wiki/Atomic_clock#/media/File:FOCS-1.jpg
  4. https://www.open-electronics.org/a-gps-clock-using-a-12-neopixel-ring/

Appendix: LF radio antennae of NIST radio station (photo credit: NIST)

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