The disclosure is directed to techniques that use a data communication system such as ADS-B to provide an output to alert an aircraft operator of an incorrect barometric pressure setting for a pressure altimeter, and provide the correct altimeter setting. For example, the system may compile the ADS-B Out data from other aircraft operating near a first aircraft to provide the barometric pressure setting in use by the other aircraft. A system of this disclosure may identify the altimeter setting used by majority of the other aircraft in a region of airspace. If a first aircraft's current barometric altimeter setting is different from the setting of the majority of the nearby aircraft, then the system may generate an output to alert the operator of the first aircraft of a potential incorrect altimeter setting as well as provide a suggested barometric altimeter setting.