I came across this consumer device. Not sure if anyone has experience with this or anything else?
“underwearables” 
Could be useful if you’re undergoing treatment for erectile disfunction, or for “research”?
I’d also be very amused if they were able to estimate sleep phases more accurately than Oura…
I think this device is used for maintaining an erection, not detecting an erection. You might want to consult with a urologist before strapping this on at night because one of the common warnings with these types of products is nerve damage and an associated loss of sensation from excessive use.