Imaging device, monitoring device, and electronic appliance

An imaging device comprising:

• a pixel comprising a photoelectric conversion element and a transistor;
• a first circuit configured to obtain a first image data that is analog data from the pixel, obtain a second image data that is analog data from the pixel after obtaining the first image data, compare a current value corresponding to a difference between the first image data and the second image data with a reference current value, and generate a trigger signal based on a comparison result;
• and
• a second circuit configured to obtain a third image data that is analog data from the pixel after generating the trigger signal and convert the third image data into digital data,
• wherein the second circuit is configured not to covert the third image data into digital data before generating the trigger signal, and
• wherein a semiconductor layer of the transistor comprises an oxide semiconductor.