How can you know if the Holter monitor stops recording?

It depends on whether the Holter monitor is a tape recorder or an electronic (digital) recorder. If it is a tape recorder, you will be able to recognize if the tape stops running – the sound of the motor will stop. If it is an electronic recorder it will be difficult, unless the display disappears due to low battery. Some electronic Holter recorders have a blinking light emitting diode which indicates that it is on.
Holter monitor is a device for ambulatory monitoring of the electrocardiogram. It records the electrocardiogram in two or more channels and the stored data is retrieved and analyzed by a computer software after completion of recording. The print out contains the minimum and maximum heart rates, abnormalities in rhythm, heart rate variability and ST segment analysis. It is most useful in the analysis of arrhythmia and less useful in documenting ischemic episodes.