In 2024, Casio Computer released the "Sa Watch," a watch specifically for sauna-goers, through crowdfunding. Approximately 2200 units sold out in nine minutes, and in 2025, the series became a regular feature. This news delighted Masamasa Hirota, an otaku who loves hot springs (and saunas to a lesser extent), and watches. Having finally gotten his hands on the Sa Watch, Hirota explores its capabilities.
This is the world's first sauna-safe watch. It is also an unprecedented watch designed to be worn completely naked. It is recommended that the heat-resistant BR1225A battery be replaced by a Casio service. Weight: 25g. Quartz movement (Cal. 5726). Battery life: approximately 5 years. Resin case (40.2mm x 35.4mm, 12.9mm thick). Water resistant to 5 bar. Heat resistant up to 100°C (when used in a sauna for less than 15 minutes). Price: 16,500 yen (tax included).
Photographs & Text by Masayuki Hirota (Chronos-Japan)
[Article published on January 16, 2025]
A really long introduction
There's an unwritten rule in the watch industry: don't bring a watch into a hot spring or sauna. The elements in hot springs can quickly damage the exterior of a watch, and the same goes for a sauna. In mechanical watches, the oils will flow at high temperatures, and in quartz watches, the batteries can't withstand high temperatures. So, with the exception of enthusiasts like me, no one brings a watch into a hot spring or sauna.
However, in 2024, Casio developed the "Sa Watch," a watch specifically for sauna use, and solicited buyers through crowdfunding. I was determined to buy one, but at that exact moment I was caught up in a mysterious meeting where I was forced to explain deadlines, budgets, and progress, and before I knew it, they were all sold out. Hey, did Momira really want a Sa Watch? And does she really want to wear it to the sauna? Didn't she just want to say she got one? If you have two, don't you think it would be a good deed to give one to Hirota? Someone please give it to me.
As this was the world's first watch that could be used in a sauna, I assumed there would be huge demand. However, Casio only prepared a little over 2000 units. Unless you're a hot spring lover (and a bit of a sauna fan) and a watch lover like me, you probably wouldn't have predicted that there would be such demand for a watch made specifically for a sauna. A Casio representative later confessed, "We never expected the sauna watch to sell this well." The approximately 2200 units sold out in just nine minutes, so it certainly exceeded expectations.
I had no choice but to search for the watch on an auction site, but so-called "scalpers" were offering it at an insanely high price. I could buy it, but as an otaku who loves hot springs (and a bit of a sauna), and watches, I don't want to taint the purity of my spirit. I want to wear the watch I bought at retail price on my wrist and grin in the hot springs (including saunas). I'm sure my friends reading this understand how I feel, right?
Every time I met with someone from Casio, I asked them to make the Sa Clock a regular product. Or rather, I asked them very persistently. Every time there was a meeting, I always added it to the report. It's possible that Casio had originally been thinking about making it a regular product, but perhaps they got fed up with the persistence of the requests from those eccentric people. Eventually, a certain person from Casio spoke with a tired look on his face, "Mr. Hirota, we're going to reproduce the Sa Clock." Yes!
What's so great about the world's first sauna watch?
The great thing about the Casio watch is that it has been designed with minimal functionality. Apparently, the development team had initially envisioned a complex, highly functional watch. However, they narrowed it down to just a clock and a 12-minute counter, and made it extremely compact. The band is also a curl band, the same type used to wind locker keys at hot springs and saunas. Casio has been striving for "high functionality" since its founding, so now they have the option of reducing functionality.
If I were to name a watch with a similar structure to the Sa watch, it would be the Jaeger-LeCoultre Reverso Memory. This model features hour and minute hands on the front of the watch and a 60-minute flyback minute hand on the back. The minute hand is constantly rotating and can be reset to zero by pressing a push button on the side of the case. It's not as complicated as a chronograph, and is sufficient for knowing the approximate time. Given its small size, I believe this is the perfect watch for a speaker.
The sauna watch also features a flyback minute hand. Normally it displays the time, but pressing the "MODE" button on the side of the case switches it to a 12-minute counter. Pressing the "RESET" button resets the hand to zero and it operates as a 12-minute counter. Operation is so simple that it needs no explanation. It's great that you can use it normally even if you're drowsy in a sauna.
What impressed me was the design, which was thoroughly designed with sauna use in mind. The case has no sharp edges, and the band attachment point is shaped in a way that hides the spring. What's more, the attachment point is so strong that even if the user were to fall in the sauna, the watch would not injure them. There are only a few parts that use metal screws, but they are designed so that they do not come into contact with the skin. This is only natural, as this is the world's first "watch designed to be worn completely naked," but it would not have come to this unless the developers actually went to saunas a lot. The packaging is simple yet to the point, as you would expect from the company that created G-SHOCK.
As an aside, I once proposed to a certain watch manufacturer the creation of something called a hot spring watch. At the time, I repeatedly emphasized that a watch worn completely naked must not only be ergonomic, but must be ultra-ergonomic, otherwise it would be dangerous if you fell over. This is something that only those who have taken a bath in an open-air bath in the middle of the night would understand. So, I think Casio is impressive for giving the watch a safe exterior.
The clock is really useful
The key feature of this watch is that it officially claims to be able to withstand 15 minutes of wearing it in a sauna below 100°C. To that end, Casio has adopted a heat-resistant battery (specifically, a high-temperature BR-series coin-type lithium battery) that can withstand temperatures from -40°C to +125°C, and has chosen a low-moisture permeable resin for the exterior to withstand the extreme environmental changes of immediately jumping into a cold bath after a sauna. It's no surprise that Casio has not only focused on appearance, but also on the internals. However, as a reputable manufacturer, they also include a disclaimer stating, "Even in the sauna, please limit wearing the watch on your wrist to 15 minutes." If you wear it longer and it breaks, it's your own responsibility. I doubt it'll break, though.
I got my sauna watch in October and have been taking it to various hot springs (which, of course, have saunas) ever since. The other day, I went to Hyaku Kannon Onsen in Higashiwashinomiya, Saitama. While I was wearing the sauna watch and counting the time, the guy next to me asked, "That's an interesting watch." When I told him it was the world's first watch that could be used in a sauna, he looked as if he wanted to buy it right away. For sauna-goers, a sauna watch that lets you instantly check the current time and how long you'll be in the sauna is a great blessing. It's true that many saunas have 12-minute counters. However, for someone like me who takes off my glasses when I go into the sauna, it's nice to have a 12-minute counter on my wrist, rather than on the wall.
By the way, if a couple has a sauna clock, they won't be late for their meeting even if they use separate men's and women's baths. I've never had the chance to do this, so it's pure fantasy, but it would probably be incredibly useful. So, all you happy couples who love saunas should buy a sauna clock. It may not be easy for you lucky people to get one, but buy one.
Although production has begun again, the Sauna Clock is still difficult to obtain. However, for sauna lovers, this watch is a must-have. And for me, the Sauna Clock was a breath of fresh air, reminding me once again how useful a watch can be. The Sauna Clock is great. Really.
