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Note 2 - Significant Accounting Policies (Details Textual) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jan. 01, 2019
Dec. 31, 2015
Retained Earnings (Accumulated Deficit), Ending Balance $ (86,361,000) $ (72,450,000)      
Cash and Cash Equivalents, at Carrying Value, Ending Balance 5,358,000 12,689,000 $ 21,352,000   $ 3,557,000
Allowance for Doubtful Accounts Receivable, Current, Ending Balance 9,000 6,000      
Impairment of Long-Lived Assets Held-for-use 0        
Cost of Goods and Services Sold, Total $ 517,000 690,000 746,000    
Standard Product Warranty, Term 2 years        
Standard Product Warranty Accrual, Ending Balance $ 0 0      
Income Tax Examination, Penalties and Interest Accrued, Total 0        
Accounting Standards Update 2018-11 [Member]          
Operating Lease, Right-of-Use Asset       $ 1,500,000  
Operating Lease, Liability, Total       $ 1,600,000  
Shipping and Handling [Member]          
Cost of Goods and Services Sold, Total $ 6,000 $ 5,000 $ 7,000