I assume when this happens, that coworker isn't silent. You can strike a conversation and get him to say something on record. Edit: and if you're concerned with

I assume when this happens, that coworker isn't silent. You can strike a conversation and get him to say something on record. Edit: and if you're concerned with running the mic all the time, then yes, you can run it all the time at no cost - see what 30 bucks buys you on Amazon.