If you’re interested in listening to your bees then you’ll want to put a mic in your hive. I did just this following the lead of beehacker.com. The mic I used was a very simple un-powered electret mic. In order to use a mic like this you’ll need to plug it into something that’s wired to provide it with power. I use an iPhone with a specially-designed mic/headphone splitter. The splitter is 10x the cost of the mic but you only need one splitter for all of your hives.