What is the temperature in in your hive? Bees need it to be 35c (95f) to successfully raise brood and over winter a temperature of at least 20c (68f) is evidence that the cluster is alive. Opening the hive is one way of checking but obviously at the expense of losing heat.
Cool Bees, a new venture dedicated to innovations in beekeeping has just been launched. Look out for the full page advertorial in January’s edition of BeeCraft Magazine.
One of their (only two at the moment) offerings is a thermometer originally designed for use in an aquarium so the sensor and cable are waterproof and can be placed in the centre of the brood area with the lcd display protected from the elements on the outside of the hive fed by the cable running through the hive entrance. Cool Bees price is £4.98 plus £1.00 p&p which is good value as we have looked for this product elsewhere and it is available from an Amazon reseller for £4.99 plus £1.98 shipping.
With a maximum temperature reading of 70c This would also be useful for use in a warming cabinet when checking for a temperature of around 45c.
You can see the BeeTemp Digital Beehive Thermometer by following this link.