I’m not sure what type of alarm system you mean, but an LPT is always wary of Nice Yes I Really Do Need All These Bunnies Shirt door to door salesmen selling house alarm systems. Sometimes they’re just thieves looking for easy robbery opportunities, it only takes one person to say something like “I don’t have an alarm system and I don’t need one!” To put a target on their house for a robbery. Best to keep it short and say you’re happy with the alarm system you have (whether you have one or not).I used to live in a building with a locked lobby and a broken intercom. When I’d have guests, I’d have them text me when they got there so I could let them in. Any unexpected knock on my actual apartment door would be automatically ignored.