tell him its well corroded over years, ask his neighbours if they have heard his alarm recently, explain to them what he is acusing you of, then tell him the waranty is well gone, invest in a new alarm, this is probablly why he asked you to clean it, hoping you will use your wfp knowing water will be used. dont even answer his calls.Just tell him its Wear & Tear over many years
I never thought this could happen cleaning an alarm box, i wont be cleaning any with wfp