INCOME TAXES - Deferred tax assets (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Bad debt reserves	$ 17,000	$ 17,000
Inventory reserves	653,000	615,000
Warranty and other reserves	77,000	78,000
Stock-based compensation	212,000	184,000
Goodwill	866,000	940,000
Acquisition costs	223,000	170,000
Net operating losses - federal	0	340,000
Net operating losses - state	77,000	91,000
Other	20,000	18,000
Deferred Tax Assets	2,145,000	2,453,000
Deferred tax (liabilities):
Prepaid expenses	(79,000)	(373,000)
Depreciation	(1,154,000)	(732,000)
Intangibles	(696,000)	(720,000)
Net deferred tax assets	$ 216,000	$ 628,000