What’s the Password? has a simple concept: To solve each of the game’s more than 100 puzzles, you have to type in the right four-digit password on a number pad. That might sound like a limited constraint. But the simplicity gives solo developer Dan DiIorio, better known as TrampolineTales, lots of room to play with clever ideas. Over the course of a few hours, the game never stopped surprising me.

Puzzle clues come in several different formats. Some are written text; the very first puzzle is a sentence that tells you what numbers to punch in. But you’ll also have to decipher four-digit codes from things like the blinking digits of a clock, nonogram puzzles, solving arithmetic, and even counting the number of teeth on a key. Clues can get a little meta, too, like ones referencing a password on the game’s cover art or information in menus.

The puzzles can be tough. I’d get a few right away, but for most, I’d have to try a few solutions to see what worked. Fortunately, there’s no penalty for wrong guesses, so you can try as many combinations as you want. Some stopped me cold for minutes at a time. If you’re stuck on a puzzle for a while, the game will give you an option to skip it, and occasionally you can get a hint.

The game is backed by a calming, jazzy soundtrack that loops a single song over and over, and it pairs well with the game’s entirely black-and-white visuals. The whole vibe made me feel like some kind of noir gumshoe. But I also found that the slow drone could help when I was stuck on a particularly tricky puzzle; my mind would occasionally wander to the meandering music, and every once in a while, that idle thinking would lead me to a puzzle’s solution.

In the end, I couldn’t solve everything. It took me about three hours to work my way through What’s the Password?, and I completed about 77 percent of the puzzles. But the game reminded me of the value of patience and a good night’s sleep; coming back in the morning with a fresh mind and coffee in hand, I usually had an easier time figuring things out. A lot of the fun of What’s the Password? was seeing what unexpected format would be thrown at me next, and that’s what gives the simple premise such depth.

^{What’s the Password? is out now on PC via Steam, iOS, and Android.}