Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 35,095	$ 38,739
Restricted cash - current	618	454
Accounts receivable, net of allowance of $231 and $180 at 2022 and 2021, respectively	4,693	5,406
Inventories, net	4,850	4,433
Prepaid expenses and other current assets	1,878	2,356
Total current assets	47,134	51,388
Property and equipment, net	3,260	2,632
Restricted cash	1,138	952
Operating lease right-of-use assets	5,644	5,735
Prepaid and other non-current assets	253	278
Total assets	57,429	60,985
Current liabilities:
Accounts payable	2,892	4,189
Accrued liabilities	1,967	2,528
Deferred revenue	6,335	6,277
Current portion of operating lease liabilities	297	268
Total current liabilities	11,491	13,262
Long-term deferred revenue	2,076	2,238
Operating lease liabilities	5,754	5,842
Other liabilities	202	219
Total liabilities	19,523	21,561
Series A - Convertible preferred stock:
Convertible preferred stock, Series A, par value $0.001; 22,386 and 22,387 shares outstanding at 2022 and 2021, respectively	5,584	5,584
Stockholders’ equity:
Convertible preferred stock, Series B, par value $0.001; 10,000,000 shares authorized, 5,610,121 shares outstanding at 2022 and 2021	6	6
Common stock, par value $0.001; 300,000,000 shares authorized, 74,647,329 and 74,618,240 shares issued at 2022 and 2021, respectively	75	75
Additional paid in capital	535,209	532,641
Treasury stock, 4,015 shares at 2022 and 2021	(206)	(206)
Accumulated deficit	(502,762)	(498,676)
Total stockholders’ equity	32,322	33,840
Total liabilities and stockholders’ equity	$ 57,429	$ 60,985