Hi.

Is there an instrument gadget that monitors/tells if a person is dehydrated ?

Usually evident without monitors, but a refractometer can confirm it when used on a urine sample. Even then, most times visual inspection will work to detect highly concentrated urine. If someone is conscious and verbal, it's usually easy to determine by just asking about symptoms. There's also wearable monitors that check skin capacitance. (IIRC, steelworkers and some miners use them in intense heat conditions)

Generally if you are healthy and feel dehydrated, you are, at least a little bit. Just a matter of drinking a tall glass and see if you feel better. For me, headachy plus general achiness is a common symptom, often before intense thirst.

1 hour ago, TheVat said:

Usually evident without monitors, but a refractometer can confirm it when used on a urine sample. Even then, most times visual inspection will work to detect highly concentrated urine. If someone is conscious and verbal, it's usually easy to determine by just asking about symptoms. There's also wearable monitors that check skin capacitance. (IIRC, steelworkers and some miners use them in intense heat conditions)

Generally if you are healthy and feel dehydrated, you are, at least a little bit. Just a matter of drinking a tall glass and see if you feel better. For me, headachy plus general achiness is a common symptom, often before intense thirst.

Salty mouth is a sign as well.