I have emergency lights, do I need a siren?

I am a volunteer fireman in Louisiana in 1 town and a 1st responder in 2, i have 1 set of red lights for my car, but the only audio I have is my stock horn with a a few choice words from myself when they don't pull to the side. I am looking at prices for sirens, and I am planning on getting 1, but I want to make sure that it is legel for me to have 1. Can anyone help me with my problem?