A device adapted for insertion into one or more of an esophagus, a stomach, an intestine and a colon for detecting a blood-oxygen level associated with at least one mucous membrane region in said one or more of the esophagus, the stomach, the intestine and the colon is disclosed. The device includes a flexible and elongated main body, and a blood oxygen level detecting unit. The blood oxygen level detecting unit includes one or more blood oxygen level detecting modules disposed on the main body and capable of generating one or more signals associated with the blood oxygen level(s) of one or more mucous membrane regions nearby the blood oxygen level detecting module(s).
