Honestly don’t know. It’s certainly not a makom sakana without one. And as those in the apartment building last week proved, it’s worthless in case of explosion r”l. It’s worthless if the fire starts between the alarm and the bed r”l. And it’s worthless in case of flood r”l. So every room should be equipped with two smoke alarms, an early explosion detector, a flood detector in every room, a message from recent tragedies.
I have one (gasp).
Whether I’m mechuyav to have one? I really don’t think so. I’m mehader in mitzvohs. But I didn’t buy one because it’s a sakana without one. And to my humblekite, proper hishtadlus would be to make sure appliances are not defective. And I’m mispalel to HaShem to protect us from ANY mishaps. At the end of the day (beginning and middle too) HE is the source of everything.
Case of medicine you stated? We’re so very far from medicines mentioned in Gemarah. Is there some medicine around today, for delicate persons, to put under the pillow, and have the power of the herbs (or whatever) reach the affected area? Doubt it. Brain surgery (wow!) where the skull is softened and cut with a knife? Never heard of that procedure (don’t forget – I’m an accomplished, accredited doctor, surgeon too). Other remedies – astounding!! Go the hospital, the fish bone extraction ward, and watch them gasp as you perform the chad chad or ninatzta kemachat procedure. So no, we’re not as advanced as they were. We’ve made many other marvelous strides in medical, pharmaceutical and many other fields, yet they were, in a sense much more advanced then.