Square D  model Qo115AFIC, single pole mini 15 amp  arc-fault breaker.
Able to sense and switch off the circuit if an electrical arc occurs,
commonly used on circuits for bedrooms.
This is a generation 1 version which is not allowed for use in new construction but can be grandfathered in to replace a non functional breaker of the same type and version.
Available new in package for $75