While unboxing the Ember Mug 3, I pondered the hubristic battle humanity has long waged against nature. Ember makes mugs that keep your drinks hot for hours longer than nature would otherwise ordain. Coffee and tea are among the quiet luxuries that get me through each day, but I'm a torturously slow drinker who will nurse a flat white for several hours. The prospect of a mug that keeps my drinks optimally heated was therefore catnip to a self-styled cappuccino connoisseur. When Ember reached out with the third in its series of smart sippers, I snatched the opportunity to try it out, especially since the Mug 2 has been a stalwart on our gift lists like the best gifts for teachers and for remote workers. But as Prometheus before me learned, there are unintended consequences for stealing fire.

Now, it is 3PM and a cup of coffee sits on my desk, two-thirds full and exactly 136 degrees Fahrenheit according to the Ember app. With a capacity of 14 ounces, the Ember Mug 3 is heavier than I expected, weighing more like a 24-ounce thermos to accommodate the tiny computer and heating element in its base. It feels accordingly sturdy, soft in the hand but with a satisfying metallic clink against my fingernails, and it is top-rack dishwasher safe. A thin, pale LED under the logo informs me the cup is on when I'm not looking at the app. It sits on an included coaster, which is actually the cup's charging pad. That means you'll need to avoid spilling liquid on the coaster, a countercultural coup against the very concept of coasters.

The coaster-charger is a neat trick, but not a very robust one. When I first used the Mug 3, I set it to 145 degrees  — the top end of the supported temperature range and also the ideal temperature for brewed coffee  — and set it down on the coaster with about 30 percent battery life. The battery died within two hours, and the slow charging speed provided by the coaster proving too little to sustain it. With a full battery, the mug seemed to keep a much better pace, and I consistently drained drinks, not batteries. There's probably a good reason Ember went with a two-pin pogo charger rather than the more robust Qi standard, likely to avoid generating excess heat, but I still wish it were here. I also wish the coaster used a USB-C connector rather than a hard to replace barrel plug for wall power.

Ember seems acutely aware that battery is a concern. You'd be forgiven for thinking the included lid has extra batteries in it, since the marketing copy advertises three extra hours of life when using it. But no, it's a normal mug lid. The extra battery life comes from the trapping of heat. A device designed to defy thermodynamics must nonetheless defer to them.

My biggest gripe with the Mug 3 is its app. Whenever a piece of tech with a mandatory app comes across my desk, the experience invariably becomes more about the app than the hardware. It's no different here. Setup was seamless, and my hopes were further raised by the ease with which I could dial in my temperature settings. But from that point, things deteriorated. Often, I'd change the temperature or turn the Mug 3 off in the Ember app, only to later find it still locked to a prior setting. And, as of this writing, I must re-pair the mug to my phone's Bluetooth about half the time I try to use it. Several times, the app presented me with an error message on launch. For reference, I use an Android phone and cannot speak to the experience on iOS.

I also wish there were some way of adjusting the mug's temperature more granularly on the device itself. If the companion app isn't your cup of tea, your cup of tea will instead be one of a few temperature presets invoked by pressing the single button on the bottom of the mug. Yes, that underside button placement becomes a frustratingly risky endeavor when the mug is full of liquid.

As for what the Ember Mug 3 does to drinks, basic chemistry tells us that heat should change the molecular structure of a beverage, and therefore also its taste. Indeed, coffee tastes subtly different when kept hot in the Mug 3. After an hour at 140 degrees, a pour-over brew of Columbian medium roast that I made from freshly roasted beans lost some of its fruity top notes and developed a more bitter, over-extracted taste. After I considered that I wouldn't keep a coffee pot that hot, I set the mug to 130 degrees the next morning, and eventually settled on 120 by midweek. Espresso and milk drinks weren't so temperamental, and a latte in the Ember tasted just as good two hours after the barista handed it to me.

Black tea, which is less sensitive to high temperatures, fared better, especially at medium temperatures. The best was herbal tea  — my nightly cup of Sleepytime stays at a perfect sipping temperature, and the maintained heat actually seems to improve the flavor over time. I take all my drinks without sugar, and I add just a splash of whole milk to brewed coffee. Your mileage may vary in accordance with your drink preparations.

What cannot be as easily assessed is how magical it feels to have a hot beverage hours after you know it should be tepid. No matter how often I used the Mug 3, every sip sent me for a loop. It's like when you think you're about to drink flat water and it's sparkling instead. I found working my desk to be a more pleasant experience with the Ember mug by my side, and as we head into fall and winter, I'm excited to keep it there.

The beverages may go down relatively smooth. The price does not. The Mug 3 retails for $150, which is far too rich for most blood. For reference, the original Ember Mug was $80 back when it debuted in 2017. Accounting for inflation, that's around $108 in today's money. Fortunately, retailers like Crate & Barrel offer cheaper alternatives. For about $40 less, I can get the Ohm Ui Inkstone, an Ember lookalike with an even more naturalistic and minimal aesthetic that looks right up my alley. Thankfully, we've seen Ember Mugs get steep discounts around Black Friday in years past, so it's worth keeping your eyes peeled for a deal in the coming months.