At this time of year here in Hampshire, it is generally too cold for the bees to fly and so they largely stay inside the hive, bundled into a loose cluster with the Queen at the centre. The clustering enables the bees to keep warm whilst at the same time minimising the consumption of the stores of honey and pollen gathered during the previous spring and summer.
This means it's difficult for the beekeeper to sometimes know if the colony is still alive inside the hive until they emerge on a warmer day later in the early spring and even then, seeing one or two flyers is no guarantee that the rest of the colony is happy and healthy.
On some thin-walled wooden hives you can sometimes place your ear to the outside of the hive and listen for the bees, but on my highly insulated polystyrene hives, this is very difficult.
So some time ago, I invested in a simple stethoscope bought on eBay for £4.99 and as ably demonstrated by my assistant in the picture, it's a great way of listening to the goings on inside the hive. A short, sharp tap on the outside of the hive results in a distinct answering buzz from the bees inside lasting a second or two before the sound stops and they return back to the cluster. This process is a very satisfying way of knowing that the colony inside is OK and gives the beekeeper confidence that they are doing the right thing.
You can also use the "tap and listen" process anytime of the year to determine if the colony is "Queen-right" or has an active, healthy Queen. If the buzz response to the tap on the outside of the does not die away quickly, it can be a sign that the Queen is not present and reflects the bees agitated state without a Queen to lead them.