BALANCE SHEET COMPONENTS - Schedule of property and equipment, net (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ (2,315)	$ (2,242)
Property and equipment, net	416	407
Depreciable Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Total in service	2,731	2,577
Property and equipment, net	416	335
Research and development equipment
Property, Plant and Equipment [Line Items]
Total in service	1,897	1,826
Office and computer equipment
Property, Plant and Equipment [Line Items]
Total in service	494	494
Autos
Property, Plant and Equipment [Line Items]
Total in service	54	54
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total in service	46	46
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total in service	240	157
Construction in progress
Property, Plant and Equipment [Line Items]
Total in service	$ 0	$ 72