Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities:
Net loss	$ (2,381)	$ (2,880)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	207	234
Amortization of debt discounts and financing issuance costs	65	130
Provision for doubtful accounts and other adjustments to accounts receivable	22	74
Provision for excess and obsolete inventory	(6)
Stock based compensation	164	446
Change in fair value of warrant liability	139
Change in operating accounts:
Accounts receivable	(232)	183
Prepaid expenses and other assets	112	208
Accounts payable and accrued liabilities	(59)	(695)
Deferred revenue	110	586
Net cash used in operating activities	(1,859)	(1,714)
Investing activities:
Capital expenditures	(16)	(13)
Net cash used in investing activities	(16)	(13)
Financing activities:
Proceeds from stock sale for employee stock purchase plan	3	2
Proceeds from common stock offering, net of expenses	4,462
Proceeds from (repayments of) related-party short-term notes payable	(1,000)	2,000
Dividends paid on preferred stock	(141)
Net cash provided by financing activities	3,324	2,002
Net increase in cash and cash equivalents	1,449	275
Cash and cash equivalents, beginning of period	2,205	2,229
Cash and cash equivalents, end of period	3,654	2,504
Supplemental disclosures of cash flow information:
Cash paid for income taxes	5	2
Cash paid for interest expense	111	$ 120
Supplemental schedule of non-cash financing activities:
Issuance of common stock warrants in connection with stock offering	$ 2,908