I did not have any leads or halter for my 3 Holter monitor tests. I just had an adhesive patch about 1.5 inches by 6 inches. The actual device is 1 inch by 4 inches by 0.5 inches thick. It depends on just what the doctor wants to monitor. In my case we were looking for Afib and premature Ventricular Contractions (PVCs).
I've used a Boston Scientific "Mini Remote Cardiac Monitor" 3 times. The first 2 times a technician installed it on the center line of my chest in the Electrophysiologist's office. The 3rd time Boston Scientific mailed it to me, and I installed it myself. See
https://www.cdx.bostonscientific.com/us/en/patients/cardiac-monitor/bodyguardian-mini.html
I wore the device 24x7, kept it on in the shower, etc. I only noticed the device when I was changing clothes. After my monitor test was complete (7 to 14 days) I mailed the device to Boston Scientific; they read the data from the device, prepared a report, and sent that report to my Electrophysiologist.
Note: I carefully cleaned my chest to insure good adhesion of the device. If the adhesive had come loose, I would have had to replace the adhesive backing.