Most medical students will remember the smell they are presented with on their first time observing a surgical operation which utilises cautery (diathermy). Electrocautery become a very common surgical technique as it provides a safe and highly effective method of haemostasis (clotting) and tissue destruction during surgery. It involves a direct (monopolar) or alternating (bipolar) current being passed through a resistant metal wire electrode, which generates a large amount heat. This heated electrode is applied to tissues which will cut through tissue and cause haemostasis of blood vessels. A cautery device may utilise a monopolar or bipolar current. Monopolar devices look a bit like a pen or probe with two buttons. In a monopolar device, the electrical current oscillates between the surgeons probe, through the patients body until meeting a metal plate often on the patents thigh, which completes the circuit. Monopolar devices require a very large current to work. ​ The two buttons on a monopolar probe indicate 'cutting' and 'coagulation'. Cutting uses a continuous waveform at a low voltage. Water is vapourised from the tissues which enables a clean cut. Coagulation uses a pulsed waveform at a higher voltage. This provides enough heat for thermal coagulation and thus, haemostasis or clotting. A bipolar device looks a lot like a set of forceps. This device contains two electrodes, between which current is passed. When conducting an operation on a smaller area (e.g. digit), bipolar cautery is preferred to avoid the larger monopolar current focusing over a small area. Bipolar devices also do not interact with implanted electrical devices, making them the tool of choice in patients with devices such as cardiac pacemakers, ICD’s and deep brain stimulators. An electrocautery device can be capable of reaching temperatures of 100-1200 degrees C, and may be used with a variety of tip types depending on the use. ​ A bipolar machine is often operated with a button at the surgeons feet underneath the drapes. This allows the surgeon to stand on the button to turn it on and stand off the button whilst not in use.  ​ In summary, cautery or diathermy uses one of two techniques depending on the requirements. Monopolar diathermy is often used in larger operations whereas bipolar is often used on smaller surgical sites or when monopolar is contraindicated. Cut and coagulate are two common modes on these instruments and utilise different voltages to achieve their desired effect.