It’s hard to say what, precisely, makes a design timeless. Some classic gadgets are simply beautiful, while others remain functional years after they come out. The list of truly timeless products in tech is small, but there’s one name that looms large: RobCo Industries’ Pip-Boy. Sure, it’s relatively simple, and some of its features only work if you’re stuck underground. But when a design hasn’t changed for 200 years, you know it’s doing something right.

For those who have been living under an irradiated rock, a Pip-Boy is a wrist-worn computer that — despite originally being meant for the pre-war world and, later, life inside of a Vault-Tec vault — has become an indispensable tool for survival out in the wasteland. It’s large and rugged, though not particularly heavy or uncomfortable, and is outfitted with plenty of satisfyingly chunky dials and buttons. From an aesthetic perspective, it’s surprisingly versatile, pairing with everything from a Vault-Tec jumpsuit to raider armor. You never really have to worry about when and where it’s okay to wear one.

The Pip-Boy is dominated by a monochrome always-on display. What the screen lacks in pixels, it makes up for in accessibility; it’s bright and clear enough to view anywhere, whether in the blinding sun of the Mojave Wasteland or the dank depths of a Yao guai cave.

And you’ll definitely want to check it regularly because the Pip-Boy tracks all kinds of useful health information. The display will let you know not only when you need a Stimpak but also where on your body to apply it. And — perhaps most importantly — it has a built-in dosimeter that audibly lets you know when there’s too much radiation around. Unfortunately, while it’s great for life-critical information, the Pip-Boy does skimp when it comes to more standard health features. It doesn’t even have a step tracker.

But it’s also more than a health device. The Pip-Boy’s other major use is as a GPS. The maps feature helps you stay on the right path while hunting a bounty or searching for out-of-the-way settlements, and the new AirTag-like tool makes it possible to track small objects — like, say, a dismembered body part that is of great importance to the Brotherhood of Steel — across large distances. The wasteland may be dangerous, but it’s pretty hard to get lost if you have a Pip-Boy equipped.

The rest of the functionality is a smattering of basic but useful features: a flashlight for navigating in the dark, simple games for rare moments of downtime, and the ability to look at photos (despite the fact that the Pip-Boy doesn’t have a built-in camera). None of these are must-haves, but they do give the device a slight leg-up over the competition (not that there are any competing devices anymore).

What’s perhaps most impressive about the Pip-Boy’s success as a survival tool is that it wasn’t originally designed for surviving a post-apocalyptic wasteland. It was created in part for life in an underground bunker, which means that if you somehow find yourself in a vault, the Pip-Boy has some added functionality. There are smarthome features that let you open doors with your wrist (though, naturally, the device only supports the Vault-Tec standard), and a messaging app for sending notes and tasks to fellow vault dwellers. Sadly, these features aren’t much use once you head up to the surface.

Really, the best thing you can say about the Pip-Boy is that it just works. Centuries after it first launched, the device remains not only functional but vital. You never have to worry about a software update degrading the experience or whether the radiation sensor is accurate. And when you’re in a life or death situation — which, let’s face it, is a daily occurrence on the surface — that reliability never gets old.

The biggest problem? Availability. Unless you’re born in a vault or happen upon the carcass of someone who was, Pip-Boys are in short supply.