Whenever execution of last SQL batch leaves open transactions, SSMSBoost will show floating information window with the reminder.
There will be one reminder window shown per SQL Editor tab. Reminder can be closed or will close itself when @TRANCOUNT reaches 0.
Feature re-uses native SSMS functionality, that checks open transactions whenever you try to close SQL Editor window with open transactions.
Due to this fact we do not show number of open transactions (native function returns only "yes" or "no").
You can always check number of open transactions using SELECT @TRANCOUNT statement.
You can disable this functionality in SSMSBoost settings->Transactions guard