Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Safety Siren Pro Series 3: lengthy equilibration period ...

We located this detector per instructions in our basement. The inital reading at 48 hours was 9.5 pCi. This increased to 9.9 at 52 hours and thereafter dropped steadily at a rate of 0.1 every 1 hour. At 73 hours the reading is (now) 7.4 pCi/liter. One explanation for this, is the occurence of one or two very large spikes in radon levels which temporarliy increased the running average. Another, I think more likely, explanation is that the device is not working properly, at least during the inital week. As the readings should have been accurate from 48 hours on, I am rather skeptical regarding the reliability of this detector, and may decide to return it. We are doing canister measurements in parallel.