Income Taxes - Schedule of Components of Deferred Tax Assets and Deferred Tax Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Deferred tax assets (liabilities):
Capitalized inventory costs	$ 103	$ 204
Inventory write-downs	815	991
Accrued warranty	78	53
Deferred profits		1
Accruals and reserves not currently deductible	1,827	2,913
Stock option expense	832	806
Federal net operating loss carryforwards	20,365	18,445
Foreign and state net operating losses	285	231
Book vs. tax depreciation and amortization	(1,724)	(1,465)
Foreign tax credits	1,207
Other deferred tax assets	135	120
Total deferred tax assets	23,923	22,299
Valuation allowance	(23,292)	(21,733)	$ (23,900)
Deferred tax assets, net of valuation allowance	$ 631	$ 566