INCOME TAXES - Deferred tax assets (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Bad debt reserves	$ 24,000	$ 25,000
Inventory reserves	789,000	762,000
Warranty and other reserves	45,000	74,000
Stock-based compensation	200,000	205,000
Goodwill	755,000	852,000
Acquisition costs	201,000	212,000
Net operating losses - state	166,000	168,000
Other	98,000	51,000
Less valuation allowance	(287,000)	(316,000)
Deferred Tax Assets	1,991,000	2,033,000
Deferred tax liabilities:
Prepaid expenses	(238,000)	(260,000)
Depreciation	(914,000)	(1,113,000)
Intangibles	(490,000)	(434,000)
Net deferred tax assets	$ 349,000	$ 226,000