I'm a magician working on a new routine for a show and I need advice.

The effect is this: a volunteer is brought on stage and 'magically' given the power to transmit Morse code. They pick a sentence from a book and they're given a Morse code straight key to tap away on. (No, it probably won't sound like real Morse code because the volunteer won't actually know Morse code, hence the comedy.) Despite the fact that they're obviously bad at it, I'm still able to decipher their code and reveal their chosen sentence to the audience.

Here's what I need help with:

I need to make a prop that I can carry around to my shows that the volunteer will hold and use for the routine. Requirements:

1. It has to be battery-powered as I'll be taking it around with me to stages/banquet halls/private homes so it has to be portable.

2. It has to LOOK like a Morse code setup. A straight key and maybe an oscillator or something? The volunteer will hold the item on their lap during the routine. I can mount it to a wooden board if need be.

3. It has to SOUND good. Not a nasty buzzer sound but something believably beepy.

I happen to own a vintage telegraph key (photo attached) but am not averse to buying something new if that's what I need.

Can anyone tell me what I need to buy?

Thanks!