INCOME TAXES - Reconciliation of Expected Provision for Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of expected provision for income taxes, computed by applying the U.S. federal income tax rate to income before taxes, to income tax expense
U.S. federal income tax rate (as a percent)	21.00%	34.00%	34.00%
Expected provision for federal income taxes		$ (178,000)	$ (23,000)
State income taxes, net of federal benefit		2,000	7,000
Non-deductible meals, entertainment, and life insurance		29,000	27,000
Research and development credit		(38,000)	(32,000)
Change in valuation allowance		16,000	15,000
Tax rate change adjustment related to Tax Reform Act		(115,000)
Prior year true-ups and other		(14,000)	2,000
Income tax expense		(298,000)	(4,000)
Deferred tax liabilities:
Accrued vacation		19,000	32,000
Inventories reserve		46,000	66,000
Allowance for doubtful accounts		2,000	4,000
Allowance for sales returns		9,000	15,000
Research and development credit carryforward		131,000	77,000
Accrued self-insured medical		1,000	3,000
Property and equipment		(242,000)	(499,000)
Intangible assets		(65,000)	(92,000)
Net operating loss		40,000
Other		6,000	8,000
Valuation allowance		(91,000)	(60,000)
Net deferred tax liabilities		$ (144,000)	$ (446,000)