We present a scalable Do-It-Yourself (DIY) fabrication workflow for prototyping highly stretchable yet robust devices using a CO2 laser cutter, which we call Silicone Devices. Silicone Devices are self-contained and thus embed components for input, output, processing, and power. Our approach scales to arbitrary complex devices as it supports techniques to make multi-layered stretchable circuits and buried VIAs. Additionally, high-frequency signals are supported as our circuits consist of liquid metal and are therefore highly conductive and durable. To enable makers and interaction designers to prototype a wide variety of Silicone Devices, we also contribute a stretchable sensor toolkit, consisting of touch, proximity, sliding, pressure, and strain sensors. We demonstrate the versatility and novel opportunities of our technique by prototyping various samples and exploring their use cases. Strain tests report on the reliability of our circuits and preliminary user feedback reports on the user-experience of our workflow by non-engineers.