Find the main control box, open it and you will find a battery (about 4x4x4 inches), with 2 wires on the top. remove the leads from the battery-
Then unplug the transformer powering the unit-(this could be located almost anywhere, so you may need to look for it).
This will disconnect all power from the system.

If the system is 10 years old, technology has changed quite a bit-
If you want to re-use the system, there are better units available now to replace what you had.

Thank you Steve. Just checked out the box...locked! No access.

We did unplug this, which is part of the system. Might that be the transformer?

And we now have this in place of the display.

Have we created a fire hazard? Or is it likely we have disconnected the power? I just want to make sure we are safe until I have time to call the monitoring company later in the week. I want to be able to call during normal business hours in case I need to be transferred to anyone.

The better approach would have been to decide first if calling the monitoring company is one of the options. If calling them was a choice, it should have been first. If they were never to be called, then ripping out the system or parts thereof is the way to go. Looks like the second choice is underway. Getting anyone to do anything to that system now will have costs included.

Thanks bus_driver. DH made the choice for us while I was at the grocery store, so we are kind of stuck with it now.

Still trying to figure out if we likely did cut the power, or if that hanging wire is a hazard.

No, I doubt if that hanging wire is a hazard. I think it is probably something like 18/4 low voltage cabling used for the keypad. How many conductors are inside of the jacket?

Since you have unplugged the transformer, now it's only if the battery low voltage alarm keeps "beeping" do you need to pursue this before the battery finally gives out.

As steve_fl mentioned above, open the box and disconnect the battery. If it has a keyed lock, it is probably just the standard equipment cabinet key lock used for years and the keys are readily available.

Thanks, yosemitebill, that's very helpful. There are 4 wires inside that white wire. The beeping stopped when the keypad was disconnected as that is here the speaker is. Much more peaceful around here now!

I will attemp to remove the battery on my days off later in the week. I'm just glad to hear it's not particularly hazardous.

Williamsem-
YES-The tan transformer was the transformer for the system.
Most residential alarm boxes are "locked" with a screw on the side of the box holding the lip of the cover closed over the box-
If that is the case, remove the screw and the box will open-
If it is a key lock, most can be pried open with a strong screwdriver-(as you are not going to be using this anymore, it doesn't matter if it is damaged)
There could be a "very slight" voltage still on that wire, (As the batteries were already beeping, it indicates that the battery was below 8 VDC, and dying quickly-
I would not worry about it being a fire hazard.
If you can get the box open and battery disconnected-there will be 0 VDC on that line (just to put your mind at ease).

Thanks, Steve. I appreciate the follow up. I will try to access the battery, just have to make a path to the box first! This might be the week I learn how to pick a basic lock.

While I do appreciate not hearing that insistent beeping, I wish DH had just waited until I could call the company tomorrow am. I'm just glad to hear it's not a fire hazard!