During six-month period ended March 31, 2019, the Company issued 250 shares of common stock for the conversion of approximately 250 shares of Series B Convertible Preferred Stock, respectively (See Note 11). 

Restricted Stock

The Company did not grant restricted stock during six-month periods ended March 31, 2020 and 2019. Stock-based compensation expense attributable to restricted stock was $130 and $885, and $200 and $400 during the three and six-month periods ended March 31, 2020 and 2019, respectively. As of March 31, 2020, there was approximately $700 of unrecognized compensation expense related to restricted stock outstanding. On November 23, 2019, 500 shares of restricted common stock held by the Company’s former president became fully vested upon his passing. These shares were issued during six-month period ended March 31, 2020. No shares were issued during the six-month period ended March 31, 2019.

A summary of restricted stock activity is presented as follows:

Warrants

No warrants were granted or exercised during the six-month period ended March 31, 2020.

Stock Options

As of March 31, 2020, there were stock options outstanding under the Company’s Second Amended and Restated 1997 Stock Option Plan and the Company’s Amended and Restated 2013 Incentive Stock Plan. Both plans were approved by the shareholders. The plans granted specified numbers of options to non-employee directors, and they authorized the Compensation Committee of the Board of Directors to grant either incentive or non-statutory stock options to employees. Vesting periods are established by the Compensation Committee at the time of grant. All stock options outstanding as of March 31, 2020 and September 30, 2019 were non-statutory stock options, had exercise prices equal to the market price on the date of grant, and had expiration dates ten years from the date of grant.

Stock-based compensation expense attributable to stock options and warrants was $226 and $68, and $300 and $700 for the three and six-month periods ended March 31, 2020 and 2019, respectively. As of March 31, 2020, there was approximately $960 of unrecognized compensation expense related to unvested stock options outstanding, and the weighted average vesting period for those options was 3.96 years.