Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (7,220)	$ (5,966)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	56	70
Noncash interest expense	134	119
Amortization of intangible assets	76	76
Inventory excess and obsolescence charge	405	739
Change in fair value of warrants		(36)
Stock‑based compensation expense	449	60
Change in operating assets and liabilities:
Accounts receivable	781	(579)
Inventory	(617)	(802)
Prepaid expenses and other assets	544	41
Accounts payable	(1,261)	(945)
Accrued expenses and other liabilities	(692)	(554)
Foreign currency remeasurement loss	38
Net cash used in operating activities	(7,307)	(7,777)
Cash flows from investing activities:
Proceeds from the sale and maturity of short-term investments	4,000
Payment for intangible asset		(500)
Purchase of property and equipment	(68)	(48)
Net cash provided by (used in) investing activities	3,932	(548)
Cash flows from financing activities:
Payment of initial public offering costs	(522)
Proceeds from issuance of Series B redeemable convertible preferred stock, net of offering costs		481
Proceeds from exercise of stock options	8	3
Net cash (used in) provided by financing activities	(514)	484
Effect of exchange rate on cash	(2)	(5)
Net decrease in cash and cash equivalents	(3,891)	(7,846)
Cash and cash equivalents, beginning of period	45,302	17,278
Cash and cash equivalents, end of period	41,411	9,432
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	745	793
Supplemental disclosures of noncash investing and financing activities:
Accretion of redeemable convertible preferred stock		2,025
Intangible assets in accrued expenses and other liabilities		$ 2,000
Property and equipment purchases in accounts payable	4
Issuance of common stock for early exercised stock options	$ 1