Statement of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities
Net loss	$ (460)	$ (1,732)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	383	409
Stock-based compensation	743	805
Non-cash gain on warrant revaluation	4	(6)
Non-cash interest expense	86	73
Changes in operating assets and liabilities:
Accounts receivable	(2,708)	(521)
Inventory	363	(81)
Prepaid expenses and other current assets	62	21
Accounts payable	(63)	(1,067)
Accrued liabilities	280	(435)
Deferred revenue	3,000
Lease liabilities	(39)	(21)
Net cash provided by (used in) operating activities	1,651	(2,555)
Cash flows from investing activities
Purchases of property and equipment	(309)	(64)
Net cash used in investing activities	(309)	(64)
Cash flows from financing activities
Payments on debt	(600)
Payments on finance lease obligation		(2)
Proceeds from exercise of stock options and purchase of shares in employee stock purchase plan	144
Proceeds from issuance of common stock in at-the-market offering, net of issuance costs		2,084
Net cash (used in) provided by financing activities	(456)	2,082
Net increase (decrease) in cash and cash equivalents	886	(537)
Cash and cash equivalents at beginning of period	14,599	14,487
Cash and cash equivalents at end of period	15,485	13,950
Supplementary cash flow information:
Interest paid	66	99
Operating cash flows paid for operating leases	413	486
Financing cash flows paid for finance leases		2
Non-cash investing and financing activities:
Bonus settled in shares of common stock	$ 364	$ 315