How to design card that makes sound?

[txks]

Hello

I have the mp3 of a sound. I want to create a device that would play this sound any time I want it to. IT has to be approximately the size of a business card, although it could be slightly bigger. Any time I want to play this sound, it should play it. I am thinking I would install a button and press the button. But it needs to be discreet, nobody should realize that I am doing this, so the button would be on the bottom of the card.

How would you design this? What parts do I need? I am thinking battery, speaker, wires, something to hold the mp3 file (a hard drive?) I really don't know, can you help me please?

[Cake of Doom]

I'd imagine looking into the set-up of a musical birthday card would give you a decent idea of where to start.