Emails you when an account's spend and impressions both suddenly collapse to near zero during a time it's normally active. This is your fastest signal that serving has stopped account-wide - whether it's a billing failure or a suspension - so you can jump on it straight away and get the account back live.
Requiring spend and impressions to collapse together is what makes this reliable. Impressions alone can dip on a quiet day; spend alone can dip when CPCs fall. Both hitting near zero at a normally-active hour means serving has actually stopped.
Counts as dark when below - how close to zero both must drop, versus what the account would normally have done by this time of day. Default 5% of normal, adjustable 1-25%.
Baseline window (days) - how many trailing complete days build the median daily baseline. Default 14d, adjustable 3-30.
Checks every 30 minutes; 12-hour cooldown - so a continuing outage resurfaces.