text: We ordered these because of 3 main features 1. photoelectric, 2. smoke and CO, 3 battery operated. Upon receipt it doesn't' say photoelectric anywhere. I honest to god just put out a neighbors fire last weekend and it was the early detection of photoelectric that saved his home. The alarm went off at the smoldering stage and he wasn't home but we heard the alarm, we busted in and saved the place with a large fire extinguisher. I will not chance using a detector that is not clearly photoelectric, so we immediately returned it, so not able to comment on effectiveness. Can't take the risk.