Why is the triangle on my alram system flashing and beeping?

[Megan]

I have an ADT alram system that says DSC on the front. For the last couple days the triangle has been flashing yellow and beeping but not always. Sometimes the light will be on and sometimes its on and beeping sometimes it flashes and beeps and sometimes it completely off. I only notice it when its late and there is nothing I can do about it.