{"slug": "sensor-watch", "name": "Sensor Watch", "category": "other", "category_name": "Other software", "description": "", "recommenders": 5, "commenters": 5, "warners": 0, "score": 4.287, "rising": -0.31, "first": "2025-11-12", "latest": "2026-08-19", "why": "check out sensorwatch.net or other mods that may exist for the Casio F-91W", "why_is_quote": true, "has_verdict": false, "sentiment": {"recommend": 5, "neutral": 0, "compare": 0, "warn": 0}, "spark": [2, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0], "listed": true, "loved": [], "caveat": "", "short_quote": "check out sensorwatch.net or other mods that may exist for the Casio F-91W", "kind": "", "icon": true, "domain": "sensorwatch.net", "github_repo": null, "official_url": "https://www.sensorwatch.net", "pricing": "", "aliases": ["Sensor Watch", "SensorWatch", "Sensorwatch"], "verdict": null, "praise": [{"label": "", "summary": "", "quotes": [{"id": 789856896, "item_id": 49366056, "url": "https://news.ycombinator.com/item?id=49366056", "by": "raffael_de", "date": "2026-08-19", "version": null, "stance": "recommend", "quote": "I really like my F91W case with a Sensor Watch Pro board", "excerpt": "I really like my F91W case with a Sensor Watch Pro board and accelerometer sensor. My favorite features: - Piezo alarm is much louder. - Countdown time can be incremented by tapping the watch. - LED color can be changed by adjusting RGB values. - It features sunrise/-set and moon phase info/calendar. - I changed the week day names to German abbreviations. - There are lots of intriguing watch faces that you can compil", "context": "", "use_case": "watch firmware", "switched_from": "", "story": "New Casio F-B100W \u2013 Upgrade to the iconic F-91W after 40 years"}, {"id": 770989872, "item_id": 48186867, "url": "https://news.ycombinator.com/item?id=48186867", "by": "jaywcarman", "date": "2026-05-18", "version": null, "stance": "recommend", "quote": "Check out the Sensor Watch project[1]!", "excerpt": "Check out the Sensor Watch project[1]! It's \"An ARM Cortex M0+ board swap for the classic Casio F-91W wristwatch\" that allows you to write custom firmware. [1]: https://www.sensorwatch.net/", "context": "", "use_case": "custom watch firmware", "switched_from": "", "story": "What Is Date:Italy?"}, {"id": 744809264, "item_id": 46550579, "url": "https://news.ycombinator.com/item?id=46550579", "by": "fellerts", "date": "2026-01-08", "version": null, "stance": "recommend", "quote": "Also, no F-91W thread would be complete without a mention of the sensorwatch project: https://www.sensorwatch.net/", "excerpt": "Cool project. Tip: acetone will readily dissolve the plastic parts of the card leaving the antenna(s) and chip intact. I believe a few other people have made drop-in PCBs with NFC antennas. Here\u2019s one: https://n-o-d-e.net/datarunner.html Also, no F-91W thread would be complete without a mention of the sensorwatch project: https://www.sensorwatch.net/", "context": "", "use_case": "", "switched_from": "", "story": "I hacked Casio F-91W digital watch"}, {"id": 735408736, "item_id": 45963046, "url": "https://news.ycombinator.com/item?id=45963046", "by": "mhitza", "date": "2025-11-18", "version": null, "stance": "recommend", "quote": "check out sensorwatch.net or other mods that may exist for the Casio F-91W", "excerpt": "If you're not looking for a smartwatch, but a hackable digital watch check out sensorwatch.net or other mods that may exist for the Casio F-91W", "context": "", "use_case": "hackable digital watch firmware", "switched_from": "", "story": "Core Devices keeps stealing our work"}, {"id": 734365760, "item_id": 45897860, "url": "https://news.ycombinator.com/item?id=45897860", "by": "gorgoiler", "date": "2025-11-12", "version": null, "stance": "recommend", "quote": "The astronomy face is superior as it calculates the altitude and azimuth of the selected object", "excerpt": "The astronomy face is superior as it calculates the altitude and azimuth of the selected object based on your programmed location and, of course, the current time: https://www.sensorwatch.net/docs/watchfaces/complication/#astronomy What would be even better would be to acknowledge that altitude is somewhat moot when all these objects are in the ecliptic plane \u2014 unsurprisingly Jupiter at Jovian noon is roughly where T", "context": "", "use_case": "", "switched_from": "", "story": "The history of Casio watches"}]}], "caveats": [], "who": [], "tags": [], "use_cases": ["watch firmware", "custom watch firmware", "hackable digital watch firmware"], "compared": [], "makers": [{"id": 758764224, "item_id": 47422764, "url": "https://news.ycombinator.com/item?id=47422764", "by": "matheusmoreira", "date": "2026-03-18", "version": null, "stance": "recommend", "quote": "It's an awesome project to hack on. Lots of nice people in the community. Highly recommended.", "excerpt": "Please add the Sensor Watch to the list. It's an amazing project which created an open source replacement PCB and and even a custom LCD for the legendary Casio F-91W. Fully customizable open source firmware. It's got a temperature sensor which makes it a world class temperature compensated quartz watch. I've contributed some work to it. Improved the pulsometer so it could also be used as an asthmometer which I really", "context": "Contributor and former maintainer", "use_case": "open source Casio F-91W firmware", "switched_from": "", "story": "More than 135 open hardware devices flashable with your own firmware"}], "threads": [{"url": "https://news.ycombinator.com/item?id=49362887", "title": "New Casio F-B100W \u2013 Upgrade to the iconic F-91W after 40 years", "mentions": 1}, {"url": "https://news.ycombinator.com/item?id=48162157", "title": "What Is Date:Italy?", "mentions": 1}, {"url": "https://news.ycombinator.com/item?id=47369883", "title": "More than 135 open hardware devices flashable with your own firmware", "mentions": 1}, {"url": "https://news.ycombinator.com/item?id=46489232", "title": "I hacked Casio F-91W digital watch", "mentions": 1}, {"url": "https://news.ycombinator.com/item?id=45960893", "title": "Core Devices keeps stealing our work", "mentions": 1}, {"url": "https://news.ycombinator.com/item?id=45860552", "title": "The history of Casio watches", "mentions": 1}], "sentiment_by_month": {"2025-11": {"recommend": 2}, "2025-12": {}, "2026-01": {"recommend": 1}, "2026-02": {}, "2026-03": {}, "2026-04": {}, "2026-05": {"recommend": 1}, "2026-06": {}, "2026-07": {}, "2026-08": {"recommend": 1}, "2026-09": {}, "2026-10": {}}, "versions": [], "version_unnamed": 0, "family_ref": null, "runs_on": null, "lines": [], "quotes": [{"id": 789856896, "item_id": 49366056, "url": "https://news.ycombinator.com/item?id=49366056", "by": "raffael_de", "date": "2026-08-19", "version": null, "stance": "recommend", "quote": "I really like my F91W case with a Sensor Watch Pro board", "excerpt": "I really like my F91W case with a Sensor Watch Pro board and accelerometer sensor. My favorite features: - Piezo alarm is much louder. - Countdown time can be incremented by tapping the watch. - LED color can be changed by adjusting RGB values. - It features sunrise/-set and moon phase info/calendar. - I changed the week day names to German abbreviations. - There are lots of intriguing watch faces that you can compil", "context": "", "use_case": "watch firmware", "switched_from": "", "story": "New Casio F-B100W \u2013 Upgrade to the iconic F-91W after 40 years"}, {"id": 770989872, "item_id": 48186867, "url": "https://news.ycombinator.com/item?id=48186867", "by": "jaywcarman", "date": "2026-05-18", "version": null, "stance": "recommend", "quote": "Check out the Sensor Watch project[1]!", "excerpt": "Check out the Sensor Watch project[1]! It's \"An ARM Cortex M0+ board swap for the classic Casio F-91W wristwatch\" that allows you to write custom firmware. [1]: https://www.sensorwatch.net/", "context": "", "use_case": "custom watch firmware", "switched_from": "", "story": "What Is Date:Italy?"}, {"id": 744809264, "item_id": 46550579, "url": "https://news.ycombinator.com/item?id=46550579", "by": "fellerts", "date": "2026-01-08", "version": null, "stance": "recommend", "quote": "Also, no F-91W thread would be complete without a mention of the sensorwatch project: https://www.sensorwatch.net/", "excerpt": "Cool project. Tip: acetone will readily dissolve the plastic parts of the card leaving the antenna(s) and chip intact. I believe a few other people have made drop-in PCBs with NFC antennas. Here\u2019s one: https://n-o-d-e.net/datarunner.html Also, no F-91W thread would be complete without a mention of the sensorwatch project: https://www.sensorwatch.net/", "context": "", "use_case": "", "switched_from": "", "story": "I hacked Casio F-91W digital watch"}, {"id": 735408736, "item_id": 45963046, "url": "https://news.ycombinator.com/item?id=45963046", "by": "mhitza", "date": "2025-11-18", "version": null, "stance": "recommend", "quote": "check out sensorwatch.net or other mods that may exist for the Casio F-91W", "excerpt": "If you're not looking for a smartwatch, but a hackable digital watch check out sensorwatch.net or other mods that may exist for the Casio F-91W", "context": "", "use_case": "hackable digital watch firmware", "switched_from": "", "story": "Core Devices keeps stealing our work"}, {"id": 734365760, "item_id": 45897860, "url": "https://news.ycombinator.com/item?id=45897860", "by": "gorgoiler", "date": "2025-11-12", "version": null, "stance": "recommend", "quote": "The astronomy face is superior as it calculates the altitude and azimuth of the selected object", "excerpt": "The astronomy face is superior as it calculates the altitude and azimuth of the selected object based on your programmed location and, of course, the current time: https://www.sensorwatch.net/docs/watchfaces/complication/#astronomy What would be even better would be to acknowledge that altitude is somewhat moot when all these objects are in the ecliptic plane \u2014 unsurprisingly Jupiter at Jovian noon is roughly where T", "context": "", "use_case": "", "switched_from": "", "story": "The history of Casio watches"}]}