Make her aware of the situation

Adam withdrew the remote for the vibrator from his pocket and gave his sister a quick higher powered buzz through the vibrator directly onto her clit. This caused her to let out a yelp as her sensitive nub sent waves of pleasure through her body. Upon seeing that his handy work was working as planned Adam set the vibrator to a lower setting and left it on constantly.

"The fuck do you think you're doing?"

"Well, right now nothing but in a few minutes I'll be fucking you"

"Yeah right, like I'm going to let you anywhere near my pussy"

"who said anything about your pussy?"

Adam smiled as he turned up the vibrator a notch and watched his sister fall to her knees as she reached the edge. He then abruptly shut the vibrator off denying her relief.

"Fuck, no, no I was so close"

She squeals as she desperately tries to plunge her fingers into her sopping hole but finds it impossible to get past the cold metal cage of the Chasity belt.

"Let me cum fucksake, I was up all last night thinking about fucking you, I need this"

"No what you need to do is submit, get on your knees"

This was still a risky play for Adam if she charged him and snatched both thee remote and key from him then she could conceivable escape.