is guardian alarm system and adt monitored security system afiliated together or the same company?

they are for home security

On a home security system monitored by a major company, would the in house siren go off even if you don’t pay?

I know the major alarm company would not monitor the home if you quit paying the bill or cancel service, but I think the actual sensors which are installed along with the in home hidden siren would still work. I’m asking this because the city in which I live does not send the police anymore [...]