BALANCE SHEET COMPONENTS - Schedule of property and equipment, net (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ (2,456)	$ (2,419)
Property and equipment, net	353	388
Depreciable Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Total in service	2,809	2,807
Research and development equipment
Property, Plant and Equipment [Line Items]
Total in service	1,763	1,763
Office and computer equipment
Property, Plant and Equipment [Line Items]
Total in service	808	808
Autos
Property, Plant and Equipment [Line Items]
Total in service	54	54
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total in service	41	41
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total in service	$ 143	$ 141