Maybe a rougher surface

It's also durable; I've dropped the base unit onto hard surfaces several times with no damage.

that receives the signals from those buttons, easy to understand instruction sheet, 2 nice quick-release lanyards, 2 pieces of double sided foam sticky tape to mount the holsters to hard surfaces and 2 screws that you could ostensibly use to mount the holster permanently to a hard surface

It is loud and works any where inside as well as

I can hear it anywhere in the house as well as on the deck

It's been used and worked exactly as it was supposed to.

Transmission is between the button and receiver, does not rely on some outside cellular or wifi service, works exactly as we need it to, and is reliable and simple.