Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net loss	$ (8,512)	$ (14,669)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,982	1,694
Loss on disposal of property and equipment	30	20
Stock-based compensation	3,968	3,554
Non-cash gain on warrant revaluation	(2)	(3)
Non-cash interest expense	323	290
Changes in operating assets and liabilities:
Accounts receivable	(1,808)	1,723
Inventory	2,142	1,234
Prepaid expenses and other current assets	269	149
Accounts payable	(820)	202
Accrued liabilities	(303)	(2,210)
Lease liabilities	(192)	(100)
Net cash used in operating activities	(2,923)	(8,116)
Cash flows from investing activities
Purchases of property and equipment	(320)	(861)
Net cash used in investing activities	(320)	(861)
Cash flows from financing activities
Payments on debt		(4,840)
Payments of debt issuance costs		(80)
Payments on finance lease obligation	(9)	(11)
Proceeds from exercise of stock options and purchase of shares in employee stock purchase plan	1,280	282
Proceeds from issuance of common stock in at-the-market offering, net of issuance costs	2,084	4,734
Net cash provided by financing activities	3,355	85
Net increase (decrease) in cash and cash equivalents	112	(8,892)
Cash and cash equivalents at beginning of period	14,487	23,379
Cash and cash equivalents at end of period	14,599	14,487
Supplementary cash flow information:
Interest paid	342	480
Cash paid for taxes		48
Operating cash flows paid for operating leases	1,736	1,693
Financing cash flows paid for finance leases	9	11
Non-cash investing and financing activities:
Right-of-use assets obtained in exchange for new operating leases		23
Increase of right-of-use asset and lease liability due to lease modification	545	895
Purchases of property and equipment in accounts payable and accrued liabilities	216	57
Modification of warrant		$ 36
Issuance of warrant with debt	$ 152