Statement of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net loss	$ (1,732)	$ (4,256)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	409	393
Loss on disposal of property and equipment		20
Stock-based compensation	805	704
Non-cash gain on warrant revaluation	(6)
Non-cash interest expense	73	81
Changes in operating assets and liabilities:
Accounts receivable	(521)	1,540
Inventory	(81)	(562)
Prepaid expenses and other current assets	21	93
Accounts payable	(1,067)	(955)
Accrued liabilities	(435)	(187)
Lease liabilities	(21)	(20)
Net cash used in operating activities	(2,555)	(3,149)
Cash flows from investing activities
Purchases of property and equipment	(64)	(225)
Net cash used in investing activities	(64)	(225)
Cash flows from financing activities
Payments on debt		(1,500)
Payments on finance lease obligation	(2)	(3)
Proceeds from exercise of stock options and purchase of shares in employee stock purchase plan		13
Proceeds from issuance of common stock in at-the-market offering, net of issuance costs	2,084
Net cash provided by (used in) financing activities	2,082	(1,490)
Net decrease in cash and cash equivalents	(537)	(4,864)
Cash and cash equivalents at beginning of period	14,487	23,379
Cash and cash equivalents at end of period	13,950	18,515
Supplementary cash flow information:
Interest paid	99	135
Operating cash flows paid for operating leases	486	416
Financing cash flows paid for finance leases	2	3
Non-cash investing and financing activities:
Purchase of property and equipment in accounts payable and accrued liabilities		$ 20
Bonus settled in shares of common stock	$ 315