A high-definition security system is a long-term investment in your home. You want a setup that lasts five years or more, so don't rush into buying the latest release if last year's model offers the same quality for less.
Wait for Black Friday to pick up these kits. Tech companies often drop prices on older inventory then, giving you professional-grade hardware for a fraction of the original sticker price.
That 18-month window is a hard deadline, not free money. If you have a balance left when that time is up, you will start paying interest on whatever is still owed.