when i was a kid, I think the year would have been around 1979 somebody bought me this game for Christmas and I played it constantly!!!
It was a blue handheld unit, like a calculator but bigger, with a red digital screen and buttons for the numbers 1 to 9, the object of the game was to guess a number picked by the machine (from 3 to 5 digits long, you could choose).
It would let you know if you had a correct number and if it was in the right place by beeping (I think!) I haven't met anybody else,ever who remembers anything about these. It sounds quite boring but it was very addictive and I got it down to a fine art in the end!!!