ECG devices typically detect ST-elevation myocardial infarction (STEMI) and ischemic heart disease by analyzing the electrical activity of the heart. Here's a simplified explanation of how they work:

Electrode Placement: 

Portable ECG devices have electrodes that are placed on the skin, typically on the chest, wrists, and ankles. These electrodes pick up the electrical signals generated by the heart.

Signal Acquisition: The electrodes detect the electrical impulses produced by the heart during each heartbeat. These signals are then transmitted to the device's circuitry for processing.

Signal Processing: The device's software processes the electrical signals to create a graphical representation of the heart's electrical activity over time. This representation is usually displayed as a graph or waveform on the device's screen.

ST-Segment Analysis: One of the key indicators of myocardial infarction (heart attack) is changes in the ST segment of the ECG waveform. During a heart attack, the ST segment may become elevated or depressed compared to the baseline. Spandan  devices analyze the ST segment to detect any abnormal changes.

Ischemia Detection: Ischemic heart disease occurs when there is reduced blood flow to the heart muscle due to narrowed or blocked coronary arteries. This can manifest as changes in the ECG waveform, such as T-wave inversion or ST-segment depression. Portable ECG devices  can detect these changes and alert the user to a potential ischemic event.

Alerts and Notifications: When the device detects abnormalities suggestive of STEMI or ischemic heart disease, it typically alerts the user or healthcare provider. This prompt action can lead to early intervention and potentially life-saving treatment.