Humans sleep in cycles, usually two or three cycles per night. There is a point in each cycle when waking up will leave the sleeper feeling the most rested and refreshed. After learning about this, a computer programmer designed a new smartphone alarm clock. This new alarm clock uses sensors in the smartphone to detect the sleeper’s motion and determine when the sleeper has reached the best point in the sleep cycle at which to wake up. The app can be downloaded onto any smartphone. Most users who download this app find that it does not help them wake up feeling more refreshed, but they are willing to try improved products in the future.

Which criterion did this sleep cycle alarm clock fail to meet?

It did not solve the problem.
It was not cost effective enough.
It was not readily available.
It was not safe for most users.