I can’t find a date for the “Adventure People” ambulance set, but it was a favorite of mine as a tot in the late 1970’s. You pressed that siren at the ambulance’s top and it would blare quite loudly — it was mechanical, so the toy didn’t require batteries.
What’s interesting is about all of the “Adventure People” toys are their scale. They were the same size as “Star Wars” figures, although they predated them. A lot of the 1970’s “action figures” were larger and more like dolls. (Think of how 70’s “G.I. Joes” compared with their more familiar 1980’s counterparts.)