Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash Flows From Operating Activities:
Net loss	$ (5,432)	$ (5,429)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	183	104
Gain on sale of assets	0	(1)
Warranty provision	12	(2)
Non-cash lease expense	24	25
Share-based compensation	1,029	859
Common shares issued for services	0	100
Provision for doubtful accounts	18	0
Changes in assets and liabilities:
Accounts receivable	(398)	(341)
Inventories	(304)	(924)
Prepaid expenses and other current assets	133	(9)
Accounts payable	(51)	1,168
Operating lease liability	(21)	(26)
Customer deposits	(43)	3
Accrued liabilities and other	37	(136)
Warranty settlement	(54)	9
Deferred revenue	17	156
Net cash used in operating activities	(4,850)	(4,444)
Cash Flows From Investing Activities:
Purchase of short-term investments	(4,996)	(25,003)
Proceeds from maturities of short-term investments	10,000	15,000
Capital expenditures for property and equipment	(81)	(160)
Investment in long-term deposits	(2)	0
Proceeds from long-term deposits	0	3
Net cash used in investing activities	4,852	(10,216)
Cash Flows From Financing Activities:
Proceeds from exercise of stock options	75	113
Repayment of debt	0	(100)
Net cash provided by financing activities	75	13
Net decrease in cash and cash equivalents	77	(14,647)
Cash and cash equivalents, beginning of period	4,937	16,647
Cash and cash equivalents, end of period	5,014	2,000
Supplemental Disclosure of Non-Cash Investing
Change in unrealized gain on short-term investments	(23)	2
Right-of-use asset and liability recorded during period	335	0
Patents and Trademarks [Member]
Cash Flows From Investing Activities:
Payments for intangible assets	$ (69)	$ (56)