A keyholder can be a trusted person that you nominate, who is willing to assist in the event of an alarm event. They would keep a key to your property, and need to be familiar with both the premises and the alarm system. Alternatively, you can use a professional keyholding service whereby a third-party security company holds the keys to your property.
Should you be unavailable, your chosen keyholder is who the alarm receiving centre (ARC) would call to help secure your property.