Note 2 - Summary of Significant Accounting Policies (Details Textual)		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)		Jan. 01, 2018 USD ($)
Retained Earnings (Accumulated Deficit), Ending Balance		$ (129,589,000)		$ (129,589,000)		$ (105,581,000)	[1]	$ (105,404,000)
Other Liabilities, Noncurrent, Total		305,000		305,000		327,000	[1]	132,000
Accrued Liabilities, Current, Total		$ 5,258,000		$ 5,258,000		4,605,000	[1]	4,623,000
Number of Financial Institutions		1		1
Allowance for Doubtful Accounts Receivable, Ending Balance		$ 253,000		$ 253,000		221,000
Contract with Customer, Asset, Net, Total		0		0		0
Contract with Customer, Liability, Total		182,000		182,000		$ 0
Gross Profit, Total		2,814,000	$ 1,239,000	4,161,000	$ 2,661,000
Equity Method Investment, Other than Temporary Impairment		$ 0		$ 0
Minimum [Member]
Warranty Period				1 year
Maximum [Member]
Warranty Period				3 years
Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Concentration Risk, Number of Customers		1	3	1	2
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | One Customer [Member]
Concentration Risk, Percentage		13.00%		23.00%
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Three Customers [Member]
Concentration Risk, Percentage			37.00%
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Two Customers [Member]
Concentration Risk, Percentage					26.00%
Customer Concentration Risk [Member] | Accounts Receivable [Member]
Concentration Risk, Number of Customers				2		2
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Two Customers [Member]
Concentration Risk, Percentage				49.00%		57.00%
Accounting Standards Update 2014-09 [Member]
Retained Earnings (Accumulated Deficit), Ending Balance	[2]							177,000
Other Liabilities, Noncurrent, Total	[3]							(195,000)
Accrued Liabilities, Current, Total	[4]							$ 18,000
Gross Profit, Total				$ 315,000
Increase in Change Amount Reported for Accrued and Other Liabilities Due To Separate Disclosure of Change in Other Noncurrent Liabilities [Member] | Quarter Ended June 30, 2017 [Member]
Prior Period Reclassification Adjustment					$ 53,000

[1] The condensed consolidated balance sheet as of December 31, 2017 has been derived from the audited consolidated financial statements as of that date.

[2] Change relates to cumulative effect adjustment upon adoption of ASC 606.

[3] Change relates to long-term deferred revenue related to the extended warranties not required to be recorded under ASC 606.

[4] Change relates to future costs associated with extended warranties required to be recorded on adoption of ASC 606.