  Progenitors of Type Ia supernovae (SNe) have been predicted to modify their
ambient circumstellar (CSM) and interstellar environments through the action of
their powerful winds. While there is X-ray and optical evidence for
circumstellar interaction in several remnants of Type Ia SNe, widespread
evidence for such interaction in Type Ia SNe themselves has been lacking. We
consider prospects for detection of CSM shells that have been predicted to be
common around Type Ia SNe. Such shells are most easily detected in Na I
absorption lines. Variable (declining) absorption is expected to occur soon
after the explosion, primarily during the SN rise time, for shells located
within 1 - 10 pc of a SN. The distance of the shell from the SN can be
determined by measuring the time scale for line variability.
