These would be ultra sensitive, and would be able to tune in to sound from different directions, but have the ability to block out background noise not relevant to the conversation.
Although the Senate has rejected an attempt to block debate on expanded background checks for gun sales, leaders say debate over the actual bill could last weeks.
Gun-control advocates have helped highlight these flaws, but some also worry that focus on the system's holes will be used as an excuse to block legislation requiring universal use of the background check system.