We compensate officers, directors, key employees and consultants with stock-based compensation under the Image Sensing Systems, Inc. 2014 Stock Option and Incentive Plan (the "2014 Plan"), which was approved by our shareholders and is administered under the supervision of our Board of Directors. Stock option awards are granted at exercise prices equal to the closing price of our stock on the day before the date of grant. Generally, options vest ratably over periods of three to five years from the dates of the grant, beginning one year from the date of grant, and have a contractual term of nine to 10 years.

Compensation expense, net of estimated forfeitures, is recognized ratably over the vesting period. Stock-based compensation expense included in general and administrative expense for the three-month periods ended March 31, 2021 and 2020 was $53,000 and $59,000, respectively. At March 31, 2021, 148,024 shares were available for grant under the Company's 2014 Plan.

A summary of the stock option activity for the first three months of 2021 is as follows:

	Number of Shares			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Options outstanding at December 31, 2020		15,000		$	4.76		2.94	$	2,700
Granted		—		$	—		—	$	—
Exercised		—		$	—		—	$	—
Expired		—		$	—		—	$	—
Forfeited		(1,000	)	$	4.22		—	$	320

Options outstanding at March 31, 2021		14,000		$	4.80		2.66	$	2,611
Options exercisable at March 31, 2021		14,000		$	4.80		2.66	$	2,611

There were no stock options exercised or expired and options to purchase 1,000 shares were forfeited during the three-month period ended March 31, 2021, and there were no options exercised, expired, or forfeited during the three-month period ended March 31, 2020. During each of the three-month periods ended March 31, 2021 and 2020, we recognized no stock-based compensation expense related to stock options. As of March 31, 2021, there was no unrecognized compensation cost related to non-vested stock options.

Restricted stock awards are granted under the 2014 Plan at the discretion of the Compensation Committee of our Board of Directors. We issue restricted stock awards to executive officers and key consultants. These awards may contain certain performance conditions or time-based vesting criteria. The restricted stock awards granted to executive officers vest if the various performance or time-based metrics are met. Stock-based compensation is recognized for the number of awards expected to vest at the end of the period and is expensed beginning on the grant date through the end of the vesting period. At the time of vesting of the restricted stock awards, the recipients of common stock may request to receive a net of the number of shares required for employee withholding taxes, which can be withheld up to the relevant jurisdiction's maximum statutory rate. Compensation expense related to any stock awards issued to employees is determined on the grant date based on the publicly-quoted fair market value of our common stock and is charged to earnings on the grant date.

We also issue stock awards as a portion of the annual retainer for each director on a quarterly basis. The stock awards are fully vested at the time of issuance.

The following table summarizes restricted stock award activity for the first three months of 2021:

	Number of Shares			Weighted Average Grant Date Fair Value
Awards outstanding December 31, 2020	33,330		$	4.52
Granted	7,035			4.44
Vested	(21,555	)		4.20
Forfeited	—			—
Awards outstanding at March 31, 2021	18,810		$	4.86

As of March 31, 2021, the total stock-based compensation expense related to non-vested awards not yet recognized was $59,000, which is expected to be recognized over a weighted average period of 0.98 years. During the three-month periods ended March 31, 2021 and March 31, 2020, we recognized $53,000 and $59,000, respectively, of stock-based compensation expense related to restricted stock awards.