Two main pitfalls to avoid:
_ Direct sellers who will sell you an overpriced low end detector with perhaps the added bonus of a completely unjustified maintenance contract.
_ Smoke detectors without smell. Yes, it exists! For example Elro RM144C who look as though honest than another.
This detector arrived second in the magazine Que Choisir, after Nest Protect - much more expensive - and just before the Kidde 29HLD - cheaper. The main criticism against him regarding the statement from the manufacturer that could use the same batteries for 10 years. A recommendation even more reckless than the batteries supplied with the device must be changed before 2019.
If, for whatever reason, we do not wish to purchase this unit, a tip: better not be content with the CE marking and the NF favor, why imposed controls are more rigorous.