What is this part? Is it a speaker?
It looks to me like a common ultrasound transducer.  The "40R" may indicate the intended frequency is 40 kHz, and that this is the receiver, not the transmitter.

I've seen ultrasound transducers that look just like that.

For example, here is a snippet of the datasheet of a SensComp 40LR12 ultrasound receiver: