It is essential that long-term high-quality observational measurements, which encompass the annual cycle of growth and decay of sea ice (the ice mass balance), are performed. Only then will we be able to understand the processes involved and to validate and refine ice models. Realistically, this can only be performed through the development of a basin-wide network of reliable and affordable autonomous instrumentation. SAMS developed such a system based on thermistor chains and deployed them in both the sea-ice zones in the Arctic and Antarctic. Thermistor chains (TC) have been used for measuring temperature profiles within the upper ocean and sea ice for many years, However, recent developments in sensor technology now allow for large numbers of themistors to be placed on a chain with just three wires present (common power, data bus and ground). This simplifies the cable and connector requirements and has huge benefit in terms of cost and reliability which in turn bring benefits in terms of cost, deployment, durability and size. A significant drawback of this approach is the chain’s inability to sense interfaces between air, snow, ice and water during isothermal conditions and so a novel feature of the SAMS chains is the incorporation of a heating element on each temperature sensor. Given the widely contrasting thermal conductivities of air, ice and water, we are able to distinguish between these three media, and thus determine the position of the interfaces (and thus the ice thickness) to within a few centimetres, even in isothermal conditions.