I don't know anything about advertising but sometimes I watch TV late at night and I see ads for various local and national companies and I always wondered how

I don't know anything about advertising but sometimes I watch TV late at night and I see ads for various local and national companies and I always wondered how they ever could verify that they actually are getting the air time during the time periods and channels that they are paying for, it seems like the type of thing that could easily be either intentionally or unintentionally messed up. It seems like it could be something that could be automated, a system that would listen and or watch all the channels and log the adds for the companies that subscribe to the service to insure that the broadcasters are giving the time they say they are. There is probably already something like that out there, does anyone know if there is such a thing?