I can think of a ton of things that I would like to monitor, although not everything might be possible with this particular device.
A little background. I've suffered more than ten years of some sort of fatigue. Sometimes I manage fine and sometimes (like now) I may lie in bed for hours because I don't have the energy to do anything. I've taken some medical tests but so far it's unknown what exactly I have or what could be done about it. I work part-time because I don't have the energy for a full-time job.
Back when I had the energy to exercise it seemed that I never had the capacity to exercise very intensively for months or I would fall ill, and the illness would then nullify any progress I had made. I hardly have the motivation to try anymore, though currently I find it difficult to do even minor physical exercise with resistance bands or dumbbells at home to help with my stiff muscles. At the moment I feel that my body's repairing mechanisms are limited in that I don't recover from relatively minor injuries.
My sympathetic nervous system seems to be very easily agitated. An argument with my girlfriend will cause me to get very stressed, and as a result I usually get anxiety, diarrhea and raised body temperature. My heart easily starts racing.
Fatigue and sleep
Often it's difficult for me to get up from bed in the morning. My job is thought-intensive and it's little use for me to go to work terribly tired, so I often decide that I should sleep a little more so that I'd be more productive at work. I'd like to use this device to monitor my sleep and help me decide if I've slept enough.
It also happened recently that I decided that I'm too exhausted to go to work at all. I phoned by boss and thankfully he understood, but it'd help to have an objective measure of some kind to present to him.
When I'm at work I may manage fine until it's about time for me to go. If I stay a little longer my brain often gets foggy and I end up being exhausted the rest of the evening. It's interesting that I seem to have some raise in body temperature on these evenings. It'd be helpful if the device warned me that I'm about to get too fatigued so I should leave work now and get rest. Perhaps it could do this by monitoring my body temperature.
I often feel fatigue after work but start feeling well again an hour or two before I should go to bed (at midnight). I'd like to know why this happens. Is the light from my computer monitor doing something to my circadian clock? Is turning the screen reddish helping at all? Could it actually help to turn on all the lights and pretend I'm not trying to get sleep? In any case, I'd like to use the device to monitor the effect of different amounts and wavelengths of light on my nervous system.
Like some others have pointed out, I'd like to use this device to monitor when I'm getting too stressed or agitated. Perhaps the device would detect these from the skin conductance, vigor of movement or breathing patterns. If the device would warn me I could try to distance myself from whatever I'm doing, concentrate on my breathing technique and perhaps listen to soothing music from my phone.
I often find it difficult to concentrate on what others are saying if they're talking for more than one minute. I've tried some meditation techniques but I get frustrated that my mind wanders off all the time. Could I use this device to help me with attention training by notifying me that I my mind started wandering again?
I've read a lot of psychological literature and self-help books and done kind of psychotherapy on myself. Perhaps I could find subjects I haven't touched yet by presenting myself possibly emotional stimuli (photos of my now dead grandparents, childhood photos, childhood scents...) and watching if my skin conductance indicates anxiety?
I'd like to use this device to monitor how my body is doing each day. I often feel miserable, the causes may vary and I don't always realize what's the matter with me. Sometimes I'm tired, so is there some kind of a signature that could hint me about that? Sometimes it's that I haven't eaten enough – does that show up in the device's measures somehow? Or am I actually anxious – is my sympathetic nervous system abnormally active and could the heart rate or skin conductance reveal that? Could I predict anxiety by the amount of wiggling I do (acceleremeter)?
I have some stiff muscles and they get worse if I stay in one position too long. Could I use the device to detect when that happens so I can get up and moving?
I sometimes go to a massage therapist because of my stiff muscles. I try to tell the therapist a lot if what he's doing feels like anything or not. It occurred to me once that it'd be helpful if the therapist could see in real-time whether his massage is doing anything. I'd like to present the data of this device to the massage therapist so he could use it to guide his actions.
It seems that when I eat something with a high glycemic load (lots of something with high GI) my heart starts to beat quickly. I interpret this as a sign that my blood glucose levels just shot up. There are a lot of carbohydrate sources that I can't eat a lot of because I start getting heartburn and acne, but the effects may show up only after days. I'd be interested in using a device to detect my body's response to different sources of carbs so I could better predict if it's ok for me to eat it. I would also like to know if I can somehow lessen the glucose spike (e.g. the Jaminets say that acidic sauces should do that but I haven't tried that out), and for that I'd need a device that detects changes in my body within minutes, not within days.
If I recover from my current bout of fatigue and start exercising again, could I use this device to monitor my levels of stress? It's not easy for me to tell if I'm too fatigued to exercise. If I skip exercising today, will my long-term well-being suffer? If I go will I slowly build up fatigue even if I manage today's exercise? Perhaps the time between my steps (but not necessarily the amount of them) or the vigor of my movements correlate with good energy levels?
I have some problems with my stomach but I don't know exactly what. I've considered trying some elimination diets but they seem like an awful lot of work and there are so many things I should try eliminating (fodmaps of all sorts, histamine, lactose, proteins in nuts...). It'd help if a device like this could give me warning signs.
I'd also love to use the device's measures to see how my nutritional supplements or medical drugs affect my functioning, but I'm afraid there's too much variation there and I'd need to carefully plan any experiments with myself to standardize the variables except for the one I'm interested in.