Knock, knock. Who's there?
Maybe someone can complete my bad joke. But tapping on the side of the hive might give a response.
If you put your ear against the side of the hive and give a loud rap, there should be a discernible loud hum in response.
Sadly, sometimes no one is home. The bees have died. We call this a 'dead out.' If that is the case read my blog post Hive Autopsy. There are some things you can learn about why the bees died. Learning this will make you a better beekeeper.
If you get the happy hum, hooray! The bees are still alive. The key item now is, do they have enough food stores to make it through the rest of the winter? Just like your home furnace churning away during these cold days, the bees are using more energy to keep warm.
Weigh the hive. You can do the lift test by lifting each side of the hive. This is a zen art form developed over years of experience. It is a very rough guess. You can actually weigh the hive with the Beekeeper's Scale. We do this and the data is reliable. Put a screw eye in the back of the bottom board, lift to get the weight. A weight in the 40's is okay. a weight in the 30's is worrisome.
A very quick method for emergency feeding is to add a spare box to the top and pour several pounds of sugar around the inner cover hole. Put the top cover on top of the spare box.
If you added a candy board, lift the top cover and see how much they've eaten. If they've been hungry hippos and eaten a big hole, add a candy block. Or you could put a piece of paper (the rice paper which separates wax foundation is great for this) in the hole and pour some sugar there.
You've been able to get your bees this far. Don't lose them now.