Contingency is the way to go.
Detecting unconsciousness may seem like a simple effect, but that's not all the item does. It needs to respond to that detection by triggering another magical effect, without a character's intervention. No low-level spell manages to do that. (The few sense-and-respond spells that do exist, like Magic Mouth, are explicitly denied the ability to activate any magical effects.)
Detecting unconsciousness may seem like a simple effect, but that's not all the item does. It needs to respond to that detection by triggering another magical effect, without a character's intervention. No low-level spell manages to do that. (The few sense-and-respond spells that do exist, like Magic Mouth, are explicitly denied the ability to activate any magical effects.)