5. Commitments and Contingencies Operating Leases We lease our offices and production facility under a non-cancelable operating lease in Austin, Texas that expires in April 2020. The lease contains minimum rent escalation clauses that require additional rental amounts after the first year. This lease contains one five-year renewal option. We lease certain other, less significant, vehicles and equipment. Our operating lease expense is recognized on a straight line basis over the lease terms. For the three and six months ended June 29, 2019, operating lease expense was $166,000 and $314,000, respectively. The undiscounted minimum lease payments under operating leases at June 29, 2019 are as follows: Years ending December 31, Operating Leases Remainder of 2019 $ 302,000 2020 149,000 2021 3,000 2022 2,000 2023  Thereafter  Total lease payments 456,000 Less imputed interest (11,000 ) Present value of lease liabilities $ 445,000 At June 29, 2019, the weighted average remaining lease term and the weighted average discount rate for operating leases was 9 months and 3%, respectively. Patents and Licenses We have entered into various licensing agreements requiring royalty payments ranging from 0.13% to 2.5% of specified product sales. Certain of these agreements contain provisions for the payment of guaranteed or minimum royalty amounts. Our minimum license obligations are $10,000 per year through 2025. In the event that we fail to pay minimum annual royalties, these licenses may automatically become non-exclusive or be terminated. These royalty obligations terminate at various times from 2018 to 2025. Royalty expense totaled $10,000 and $10,000 and $11,000 and $26,000, respectively, for the three and six months ended June 29, 2019 and June 30, 2018. Under the terms of certain royalty agreements, royalty payments made may be subject to audit. There have been no audits to date and we do not expect future audit adjustments to be significant.