Why idea what this is?

Have a random electric box with strange item connected to it. Located on closet ceiling, near furnace. Multimeter reads ~20 VAC across the terminals with the red wires, does not change with furnace turn on/off. House built in early '60s, previously had hard wired security system that I've removed multiple panels/sensors from. Is this part of that, or some sort of HVAC thing, or? I have not ventured into the attic yet to investigate where the small red and white wires go.

Thanks for any info!