Hi, all. I'm new here, but I'm hoping that this is the right place to ask this question. Sorry for the long post, but I wanted provide all the details in case any of them are relevant to this problem I'm having.
Last year, I bought a house that came installed with a security system. I've never really had a security system before, so I'm pretty much new to all this. Anyway, the keypad says DSC PC1500RK, and there are several 2-piece door opening detectors and a motion detector. It appears that the previous owners also subscribed to some monitoring service, which I declined to renew. I also don't have a landline, which I understand is something that's needed by many security systems (and probably this one).
Even though I didn't renew the monitoring service, the alarm system has been still operational in that whenever a door opened, there'd be this short beep-beep-beep to indicate it. And the motion detector was silent but would light up the appropriate zone on the keypads (there are a couple downstairs and upstairs). So I've been just leaving that alone, and that's been working out OK for me for the past year that I've been living here.
So today, the alarm system has started acting up, and I'm not sure why. Basically, the alarm has started going off intermittently. At irregular intervals, it'd suddenly give exactly seven very loud "weewo-weewo-weewo-..." and then shut up as if there's nothing wrong. It's done that a few times in the past year, but not repeatedly all throughout the day like it has today. The interval is around once or twice an hour. Needless to say, it's very annoying and startling.
One thing I just tried to remedy this (which may have made the situation worse?) is that I noticed that there's this circular key hole next to my front door buzzer, with red and green LEDs over it, and the previous owners left a key that fits it which is essentially like a cylinder with square teeth around its circumference and a little extra notch to indicate which way is pointing "up". I think I've had filing cabinets that came with keys like this. The key fob says "Sentry", so I thought maybe it's the master key for turning off the alarm system, so I just tried it out for the first time. Sadly, even though it fit, it didn't actually turn or light up the LEDs or stop the siren. I guess it kind of makes sense, since the key looks like it's totally generic and easy to duplicate. But I have no idea what it's for, then, and the odd thing is that now the DSC keypads all around the house are all "off" (not lighting up to show zones with activities, etc.). I'm pretty sure that my sticking in that key did that, which I don't understand. Sadly, this hasn't solved my problem, however, because the siren is still going off intermittently as before, and when it does, the keypads momentarily come back to life, and then go dark again.
At this point, I'm completely confused and don't know what to do. Anyone know what that weird circle key panel is for? Anyone know how to get the keypads to be "on" again? Anyone know what's causing this intermittent siren ringing? I'm thinking maybe there's a frayed/damaged/animal-chewed/water-damaged circuitry, or maybe a busted sensor (one of my sliding doors has a sensor that broke off a few months ago, so I just removed the piece and that seemed not cause any problems thereafter), or the system needs attending to (new battery? landline connection?), or there's an animal that's tripping a hidden sensor somewhere that I'm not aware of.
Unfortunately, the previous owners didn't really leave instructions on how to use the system; all they left me with is the master code. I don't understand why it's acting up like this all of a sudden today (beautiful sunny day, nothing out of the ordinary), but I'm not looking forward to trying to go to sleep tonight with this problem. I was thinking of maybe upgrading the alarm system and subscribing to a service anyway, so maybe I'll call one tomorrow, but I'm not sure how quickly they can come out and get it all set up, and whether that'll solve my problems (especially if it's a wiring issue and they re-use the existing wiring). In the meantime, I'd REALLY appreciate any help or advice from people who are more familiar with this stuff. Thanks!