works great in perfect operating condition: Ocean Reef M105 Surface Communication Dual Unit transmitter/receiver M-105 is a high-quality topside coms stand alone unit designed to be used with Ocean Reef full face divemasks equiped with additional comms units not included in this kit. this unit is a stand alone topside comunications receiver transmitter. Made in Italy by the reputable brand Ocean Reef, this unit allows for clear communication at the surface while divers with ocean reef transponders are underwater. Perfect for situations underwater where communication is key.