Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net loss	$ (14,709,000)	$ (13,987,000)	$ (12,308,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Write-off of inventory	1,000
Depreciation	111,000	88,000	78,000
Reduction in the carrying amount of right-of-use assets	440,000
Gain on change in fair value of redemption feature embedded in convertible notes	(52,000)
Loss on extinguishment of convertible notes	521,000
Non-cash interest expense on convertible shareholder notes	112,000
Share-based compensation	2,722,000	2,774,000	2,707,000
Changes in operating assets and liabilities:
Accounts receivable	127,000	(179,000)	(21,000)
Inventory	136,000	49,000	(56,000)
Prepaid expenses and other current assets	(198,000)	(104,000)	16,000
Accounts payable	171,000	119,000	377,000
Accrued liabilities excluding accrued interest on convertible note	922,000	240,000	415,000
Operating lease liability - current	88,000
Deferred revenue	691,000	(65,000)	96,000
Operating lease liability - noncurrent	(528,000)
Deferred rent		(4,000)	25,000
Net cash used in operating activities	(9,445,000)	(11,069,000)	(8,671,000)
Investing activities:
Purchase of property and equipment	(146,000)	(66,000)	(136,000)
Purchase of short-term investments			(1,800,000)
Maturity of short-term investments			1,800,000
Net cash used in investing activities	(146,000)	(66,000)	(136,000)
Financing activities:
Proceeds from sale of common stock and warrants	10,452,000	4,000,000
Issuance costs from sales of common stock and warrants	(1,259,000)	(200,000)
Proceeds from convertible loan payable	625,000
Proceeds from the exercise of common stock options		4,000	144,000
Net cash provided by financing activities	9,818,000	3,804,000	144,000
Net change in cash and cash equivalents	227,000	(7,331,000)	(8,663,000)
Cash and cash equivalents at beginning of period	5,358,000	12,689,000	21,352,000
Cash and cash equivalents at end of period	5,585,000	5,358,000	12,689,000
Supplemental disclosure for noncash investing and financing activities:
Conversion of notes and interest payable to stock and warrants	633,000
Issuance of restricted stock units in lieu of 2018 cash bonus	165,000
Right-of-use asset obtained in exchange for lease obligation	$ 1,505,000