Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues	$ 2,366	$ 2,302	$ 7,727	$ 6,029
Cost of revenues	1,566	1,525	5,015	4,392
Gross profit	800	777	2,712	1,637
Operating expenses:
Research and development	1,397	1,417	4,502	4,308
Selling, general and administrative	3,892	3,461	11,755	10,501
Total operating expenses	5,289	4,878	16,257	14,809
Loss from operations	(4,489)	(4,101)	(13,545)	(13,172)
Interest income	0	1	3	33
Interest expense	(419)	(433)	(1,217)	(1,245)
Other (expenses) income, net	(4)	8	2,343	8
Net loss and comprehensive loss	(4,912)	(4,525)	(12,416)	(14,376)
Accretion of preferred stock dividends	(1,044)	(967)	(3,132)	(2,901)
Net loss applicable to common stockholders	$ (5,956)	$ (5,492)	$ (15,548)	$ (17,277)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.06)	$ (0.08)	$ (0.17)	$ (0.46)
Weighted average common shares used to compute net loss per share, basic and diluted (in shares)	95,382	69,459	94,071	37,246