Today the topic of Brick Game came up again. For those that don't know, it's basically a cheap knock-off of the Game Boy with a 10×20 screen (as well as some dedicated HUD) and several games in it (which ones depends on the model). Just look it up. One interesting thing about the Brick Game is that it included sleep mode: if you turned off the system while the game was paused, when turning on it'd be back in the same exact state as when it was paused instead of resetting. Every game. Not bad for what's supposed to be a cheap knock-off.

But that's the issue. While I don't know the exact release date of the first model it's safe to say that at least in the mid-'90s it was already out there (and possibly earlier), but I can't think of any other handheld predating it that had sleep mode as well. The Game Boy line acquired the ability with the GBA, which was 2001. As far as I know Lynx didn't have it, and Game Gear definitely didn't either. The WonderSwan had Dicing Knight, but that one did it since it already had to save the state of the entire dungeon in the first place (so it was more like hybernation than sleeping). No idea about the Neo Geo Pocket, but it doesn't matter since Brick Game still predates all of them.

So huh, does anybody here know if there's any earlier handheld that had sleep mode that I may be missing? Because the idea that a cheap knock-off was the first handheld ever to include sleep mode seems ridiculous, but what I know so far seems to hint at that.

Depends on how pedantic you want to get about sleep. Does it need to be the "soft-off" where the full device appears off? What about at the chip level?

Programmable power modes have been around almost as long as there have been individual chips, with sleep, wake, and sync instructions. Individual chips with the functionality date back to the 1970s that I'm aware of, and likely are older than that. Old floating point coprocessors would sleep and resume with a hardware signal. Same with other co-processor boards like audio cards and disk controllers.

The classic Z80 had a similar low-power sleep function that retained all internal state. The processor was used in a huge number of devices. I don't recall any of the game systems that used the Z80 having a sleep mode as described, but that doesn't mean there weren't any. The massive game consoles were usually just shut down with a master power switch for a bank of machines, not a per-system soft-off button.

Among the z-80 users, I'm guessing the TI calculators (starting 1990) used that for their soft-off state since they would display your old calculations when you turned them back on. That design is from the same year as Brick Game.

Trying to remember back to my youth, the era of ColocoVision, the Apple ][, the TI-99, and the C64, I don't recall any soft-off devices among them.

I was specifically talking about handheld consoles (I thought that was obvious, guess not).

EDIT: also sleep mode differs between systems so no idea. Brick Game I think it literally shut off and just kept around the RAM (which it already needed anyway to keep the high scores and the settings). This seems to be also Dicing Knight's method, but with save memory. Not sure what the GBA does.

If you were remaking a gameboy-level device with modern parts, could you just use flash memory instead of RAM, allowing it to be powered off and retain it's state?

Except for the part that you can't do writes in a random order =P FeRAM or MRAM would be more suitable, but not cheap. Just keeping RAM powered while everything else is turned off is easier in practice (but it means the battery must remain connected, although power consumption still would be much noticeably smaller, enough to make it worth trying)