karabiner input switcher

gistfile1.txt

{
  "title": "Unicode Keypad Processor",
  "rules": [
    {
      "description": "Switch to Unicode Hex Input on Option hold",
      "manipulators": [
        {
          "type": "basic",
          "from": {
            "key_code": "left_option"
          },
          "to": [
            {
              "set_variable": {
                "name": "original_input_source",
                "value": 1
              }
            },
            {
              "input_source_selector": {
                "input_sources": [
                  {
                    "input_source_id": "com.apple.keylayout.UnicodeHexInput"
                  }
                ]
              }
            }
          ],
          "to_after_key_up": [
            {
              "input_source_selector": {
                "input_sources": [
                  {
                    "input_source_id": "^com.apple.keylayout.UnicodeHexInput"
                  }
                ]
              }
            }
          ],
          "conditions": [
            {
              "type": "device_if",
              "identifiers": [
                {
                  "vendor_id": 4617,
                  "product_id": 8721
                }
              ]
            }
          ]
        }
      ]
    }
  ]
}