Coke Piano - How did he do it?

I recently watched this video: Link to video and thought it would be a fun project as I’m new to Arduino. The only problem is that I can’t identify what he used to make it! He only showed the components for a few seconds.
I know you can use the MPR121 or whatever the name is, but I’m a little short on money. It seems like I have everything he had except the transistors, which I can buy for a buck on aliexpress anyways.

A schematic of of it for just one coke bottle would be nice! And what is the transistors used for? What do they do?

Thanks…

Just follow the link on the video and you get: http://lucaszanella.com/en/articles/cs/capacitive_sensor

Although he calls it a capacitive sensor, it is not at all. It is a touch sensor that works by you acting as an antenna and injecting interference into the transistor's base. This small voltage can turn on the transistor. It will work with any high gain transistor not just the one he used. A capacitive sensor is a totally different thing and can work behind an insulating surface, where as this does not.

Grumpy_Mike: Although he calls it a capacitive sensor, it is not at all. It is a touch sensor that works by you acting as an antenna and injecting interference into the transistor's base.

Not even that. He has a wrist strap connected to 5 V and is sensing the current flow through his body.

Russell.

Dear lord, with discrete parts?

You can get cap touch/proximity sensor IC's pretty easily now, I'm sort of surprised he didn't use one. MTCH101 for example is a single channel one - you can wire them to whatever conductive object you want to act as a sensor (I sell single channel boards, in fact, for just this sort of thing). They make an 8-channel chip too