Schedule of Financial Information Relating to Industry Segments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022	Jan. 31, 2021	Apr. 30, 2021
Segment Reporting Information [Line Items]
Total net revenue	$ 5,054,000	$ 4,633,000	$ 15,252,000	$ 13,327,000
Total income from operations	1,144,000	1,216,000	4,098,000	3,766,000
Total depreciation and amortization	106,000	108,000	319,000	297,000
Total capital expenditures	124,000	65,000	164,000	426,000
Total assets	55,103,000		55,103,000		$ 54,136,000
Security Alarm Products [Member]
Segment Reporting Information [Line Items]
Total net revenue	4,377,000	3,876,000	13,180,000	11,039,000
Total income from operations	988,000	1,008,000	3,541,000	3,119,000
Total depreciation and amortization	42,000	37,000	117,000	98,000
Total capital expenditures	113,000	65,000	153,000	307,000
Total assets	10,138,000		10,138,000		8,955,000
Cable And Wiring Tools [Member]
Segment Reporting Information [Line Items]
Total net revenue	498,000	551,000	1,553,000	1,596,000
Total income from operations	117,000	145,000	418,000	451,000
Total depreciation and amortization	31,000	31,000	92,000	92,000
Total capital expenditures
Total assets	2,378,000		2,378,000		2,534,000
Other Products [Member]
Segment Reporting Information [Line Items]
Total net revenue	179,000	206,000	519,000	692,000
Total income from operations	39,000	63,000	139,000	196,000
Total depreciation and amortization	18,000	19,000	60,000	47,000
Total capital expenditures	11,000		11,000	113,000
Total assets	661,000		661,000		667,000
Corporate General [Member]
Segment Reporting Information [Line Items]
Total depreciation and amortization	15,000	21,000	50,000	60,000
Total capital expenditures				$ 6,000
Total assets	$ 41,926,000		$ 41,926,000		$ 41,980,000