There are no significant risks involved in wearing a Holter monitor other than possible discomfort or skin irritation where the electrodes were placed.
However, the Holter monitor can't get wet, or it will be damaged. Don't swim or bathe for the entire time you're wearing your Holter monitor. However, if you have a wireless Holter monitor, you'll be shown how to disconnect and reconnect the sensors and the monitor so that you can shower or bathe.
Holter monitors aren't usually affected by other electrical appliances. But avoid metal detectors, magnets, microwave ovens, electric blankets, and electric razors and toothbrushes while wearing one because these devices can interrupt the signal from the electrodes to the Holter monitor. Also, keep your cellphones and portable music players at least 6 inches from the monitor for the same reason.