Here is a Roland KD-7 kick trigger unit in great working condition. There is a lot of wear on the unit.

Google AI says:

Key Features & Connections

• Trigger Type: Dynamics-sensitive/velocity-sensitive rubber trigger pad.
• Inputs/Outputs: Standard 1/4-inch output jack plus a 1/4-inch Mix Input that allows you to chain two KD-7 units together for a double-bass setup.
• Design: Reverse-mount configuration that uses a custom inverted/reverse felt beater, letting drummers use their preferred kick pedal