Wrist heartrate monitors are common now and some send data to another device like a cellphone. What if there was a microcontroller that received this data and manipulated a pressure actuator hooked, via a tube, to a helium balloon.
The helium balloon's expansion and contraction could made to reflect
the contractions of the heart and float, angelically, just a foot above the head. The shape of the balloon could be chosen from a set to indicator personality.
A party group dynamic would be interesting with everyone having physiological state tell. This would range from are you lying, to is there a spark or is everyone's heart in sync with this song. Or sadly, they've taken to many drinks.
If used with a large crowd, a sea of pulsing balloons jostling with individuality and cascading with collectivity might be a wonder to behold.