Found a weird horn shaped device in the attic, is it an old fan?

That's almost certainly an old **alarm siren** from a legacy security system. Back in the 70s and 80s, installers whould bolt those heavy metal horns to the joists so the sound would resonate trough the whole structure and alert the neighbors. Since there are no blades, it’s not doing anything for your airflow or ventilation. It’s strictly for making a massive amount of noise.

Those tiny wires you found are just low-voltage signal lines, prolly 22-gauge. They usally ran back to a main control box tucked away in a master closet or a utility room. If the system hasn't been used in decades, there's a 99% chance those wires are dead. You can usually just snip them and unbolt the horn to get it out of your way. It’s not part of your HVAC or any vital house function, so there's no reason to try and "turn it on" unless you want to blow your eardrums out testing it with a 12V battery.

One thing to watch out for while you're crawling around in that blown-in fiberglass: watch your footing. I’ve seen way too many people assume the insulation will support a bit of weight or provide a cushion, but you’ll go right through the drywall ceiling if you slip off a joist. I actually did that once on a job and it's a nightmare to patch. If you’re adding more R-value, it's actually better to get that hunk of metal out of there anyway so you can get a more even fill across the joist bay.

If you aren't planning on restoring a vintage security setup, that horn is basically just junk. It’s not serving any purpose for the house's current health or efficiency. Just rip it out, patch the wire holes if they go all the way through, and keep focused on your insulation levels. That'll save you way more money on your heating bill than a forty-year-old speaker ever will.

That’s a huge relief. I was honestly scared to touch it in case it was some weird electrical vent I didn't understand. Since you mentioned the control box might be in a closet, I think I acutally saw a beige metal box in the back of my coat closet that I couldn't open. If I snip the wires at the horn, is there any chance it’ll trigger some backup battery or a loud beeping downstairs? I’m trying to avoid a heart attack while I’m shimmying trough the rafters.

Honestly, after forty years, any backup battery in that beige box is going to be toast. It’s probly just a crusty brick of lead at this point. Snipping those thin wires won't trigger anything if the system hasn't had power for ages. Even if there was a tiny bit of juice left, most of those old analog systems don't have the "tamper" logic that modern ones do.

Just make sure you’re wearing a decent respirator while you're digging through that old blown-in. Moving that horn is going to kick up a ton of dust and glass fibers. Once it’s out, you can finally get a nice, continuous layer of new stuff over that spot without any thermal gaps.

If you leave it there and just blow insulation over it, you're leaving a thermal bridge where that heavy metal is bolted directly to the joist. It’s a small detail, but if you’re going for maximum efficiency, it’s better to have nothing but insulation in that bay. Plus, once you clip those wires, you can use the old wire run as a pull-string if you ever need to get a modern Ethernet cable or somthing similar from the crawlspace down into that closet. It's alot easier than drilling new holes thru the top plate later on.