Title is the word

There is a quest that gives Detect Life as a reward, it's at Treva's Watch, a fort west of Riften. Get the quest from the guy at the camp just east of the fort. I believe you have to have an alteration skill over 50 for Tolfdir at the College to sell it.

Really long-winded approach, but another way of getting it is to complete the companions quest chain, get the Hircine totem quests from Aela and then pray at the totem of the hunt...

Ok, yeah, getting alteration to 40 (I think) and then buying it from Tolfdir is probably your best bet.

Treva's watch is an simply clear an fort quest but not sure about level on enemies in it.
Detect life can be cast even with 100 mana and low alteration and no perks but will only last a couple of seconds, main issue with it is that it don't detect undead or robots as I understand but it show if humans is friendly or hostile.