My mom and dad both have pacemakers. One goes into the office once/year to have their pacemaker checked, the other goes in every 3 months. Why?

Likely one is a pacemaker/defibrillator and one is a pacemaker. The pacer/defib needs to be checked more frequently and can be done in the office or over the Internet. A pacemaker can be checked once or twice a year in the office and then once or twice over the phone. As either device gets older then it will need to be checked more frequently.