ADT monthly monitored security costs vary depend on the package you select. The basic package starts at $36.99 per month.This package is perfect for many price-conscious households who want to keep their family safe with ADT’s “round the clock” 24 hour monitoring.he basic package starts at $36.99 per month. This package is perfect for many price-conscious households who want to keep their family safe with ADT’s “round the clock” 24 hour monitoring.