We own a family run security system. We do both residential and business alarms and teach the CHL classes also. A lot of company's will hire a people to go door to door to hand out fliers and knock on doors. I have seen ADT pull up in an area in a van and dump out a bunch of people to go door to door. They may come to your door even if you have a sign as they do not know if you are being monitored or just have the sign. Do not let anyone in unless they have state identification that shows they work for an alarm company. As a side note. If you have a security system I would suggest getting radio back up in case you phones go down. We offer that here at a good price.. ADT does of course also but quite a bit higher. They have to pay for all the expensive advertising and corporate jets.
By faith Noah,being warned of God of things not seen as yet, moved with fear,prepared an ark to the saving of his house;by the which he condemned the world,and became heir of the righteousness which is by faith Heb.11:7