Electrocardiogram (ECG) has typically been done with an 12 lead device that measures the change in voltage at different terminals. This machine is rugged and sensitive to other signals. However, disruption of this technology is happening from small iPhone based devices that record ECG using just two sensors that are placed behind the phone.
A device made by the company AliveCor has been FDA cleared to be comparable in diagnosis to a GE 12-lead machine. Obviously having this machine available now makes it possible for people to carry this with them and has been used in one case to diagnose an heart patient on an airplane.
Currently, this is not a diagnostic device and is used only to monitor the heart rhythms. This is not new technology and this technology has been previously seen in other portable devices. The unique feature is that it makes it convenient and mass production makes it relatively affordable $199, though purchasing the device does require approval.