A smart doorbell lets you see who is at your door from your phone, giving you peace of mind whether you are home or out. Installation usually takes about an hour, and you can often find significant discounts on bundles during Black Friday sales.
Before buying, get at least two quotes from local handymen if you are not comfortable wiring it yourself. Compare the cost of the hardware against the labor to ensure you aren't overpaying for the setup.
That 18-month window is a deadline, not free money. If you have any balance left after the 18 months are up, the bank will start charging you interest, which can get expensive fast.