Sensor Watch Pro
Hacker ApprovedWatch replacement board in Tools & making
Open-source board that turns a cheap Casio F-91W into a hackable watch with custom firmware and temperature-compensated timekeeping. Critics say precision is not its strength.
Open-source board that turns a cheap Casio F-91W into a hackable watch with custom firmware and temperature-compensated timekeeping. Critics say precision is not its strength.
15 people gave an opinion
- recommend it
- 14
- criticize it
- 1
- approval share
- 93%
Recommended in 10 of 13 months
- November 2025: recommended
- December 2025: not recommended
- January 2026: recommended
- February 2026: recommended
- March 2026: recommended
- April 2026: recommended
- May 2026: recommended
- June 2026: recommended
- July 2026: recommended
- August 2026: recommended
- September 2026: not recommended
- October 2026: recommended
- November 2026: not recommended (month in progress)
Why it carries the badge
- 14 people recommend itNeeds 10 or more, met.
- 14 recommenders for every criticNeeds 2 to 1 or better, met.
- Recommended in 10 of 13 monthsNeeds 4 or more, met.
The same three rules apply to every product, and the badge can’t be bought. How the badge works
What people say about it
The reasons people give, with the number of comments that give each one. Open a reason to read what they said.
Why people recommend it
Each mark is one comment
Temperature-compensated, accurate timekeeping
“turning a cheap casio into a super-accurate quartz watch with temperature compensation”
Comment from 19 Aug 2026 in “New Casio F-B100W – Upgrade to the iconic F-91W after 40 years” “with a few calibrations spread out over a few months, can achieve an accuracy of”
Comment from 16 Oct 2026 in “Casio F-91W using Statecharts” “right up there with the best temperature compensated quartz watches”
Comment from 16 Jun 2026 in “Mechanical Watch” - Comment from 10 Mar 2026 in “I used pulsar detection techniques to turn a phone into a watch timegrapher”
Extra sensors and alarms
“I'll take some solace in mine supporting lots more alarms (beep when school recess ends)”
Comment from 19 Aug 2026 in “New Casio F-B100W – Upgrade to the iconic F-91W after 40 years” “I really like my F91W case with a Sensor Watch Pro board and accelerometer sensor.”
Comment from 19 Aug 2026 in “New Casio F-B100W – Upgrade to the iconic F-91W after 40 years” “Use it every day at work, makes counting respiratory frequency painless.”
Comment from 20 Aug 2026 in “New Casio F-B100W – Upgrade to the iconic F-91W after 40 years” - Comment from 20 Mar 2026 in “I love my dumb watches”
Custom firmware, open source
“An ARM Cortex M0+ board swap for the classic Casio F-91W wristwatch that allows you to write custom firmware”
Comment from 18 May 2026 in “What Is Date:Italy?” “It's an awesome project to hack on. Lots of nice people in the community. Highly recommended.”
Comment from 18 Mar 2026 in “More than 135 open hardware devices flashable with your own firmware” “also OSS as opposed to Ollee”
Comment from 19 Aug 2026 in “New Casio F-B100W – Upgrade to the iconic F-91W after 40 years” Well-known F-91W community project
“The incredible Sensor Watch after-market board is really worth a mention on a thread like this”
Comment from 11 Nov 2025 in “The history of Casio watches” “no F-91W thread would be complete without a mention of the sensorwatch project”
Comment from 9 Jan 2026 in “I hacked Casio F-91W digital watch” “Sensor Watch project gets a lot of mileage out of the Casio F-91W display.”
Comment from 15 Jun 2026 in “Not mine, but it's a website where you can use a segment display”
What people warn about
Each mark is one comment
Limited precision
“precision isn't its strength ... it's precise enough for me anyway”
Comment from 19 Aug 2026 in “New Casio F-B100W – Upgrade to the iconic F-91W after 40 years”
What people said
21 of the 24 comments that mention it, newest first. Each links to the original comment.
“with a few calibrations spread out over a few months, can achieve an accuracy of”
“Use it every day at work, makes counting respiratory frequency painless.”
“I love the USB design (the side of the board fits inside a USB micro B cable).”
“precision isn't its strength ... it's precise enough for me anyway”
“also OSS as opposed to Ollee”
“I really like my F91W case with a Sensor Watch Pro board and accelerometer sensor.”
“turning a cheap casio into a super-accurate quartz watch with temperature compensation”
“I'll take some solace in mine supporting lots more alarms (beep when school recess ends)”
“right up there with the best temperature compensated quartz watches”
“Sensor Watch project gets a lot of mileage out of the Casio F-91W display.”
“That's exactly what I'm looking for.”
“An ARM Cortex M0+ board swap for the classic Casio F-91W wristwatch that allows you to write custom firmware”
“my experience with a sensor watch has been terrible”
“Battery life measured in months, if not years.”
“That's all the sensors I need in a watch as of now”
“It's an awesome project to hack on. Lots of nice people in the community. Highly recommended.”
“Mine loses time every year instead of every day or every month.”
“I would much rather go for a Sensor Watch Pro than a Pebble”
“no F-91W thread would be complete without a mention of the sensorwatch project”
“Seems very tedious to actually use, but very cool to have it in the unassuming wristwatch.”
“The incredible Sensor Watch after-market board is really worth a mention on a thread like this”
Counts come from 1,795,640 Hacker News comments, November 2025 to November 2026. How we count. Report a mistake.