She's going to tie a bell around his wrist, so if he does get up, the bell will wake her up, and she can catch him before he gets out.
6 seconds sound clip from The Honeymooners (1955) - The Sleepwalker sitcom.
You can hear this line at 00:07:23.518 in the Blu-ray version of the TV Series.
Quote context
[...]
- If he had any brains, he'd go to the hospital like the doctor said.
- Well, look, why don't we lend him some money?
- Us?
- Yes, us. We got money in the bank, haven't we?
- Yes, we have money in the bank. $3.31.
- $3.31? Well, what do you do with all the money?
- Well, she should have listened to me, and put the tacks on the floor.
- Oh, no! No, sir! I'm not going!
- Oh, Ralph, I didn't come down for that.
- Ed didn't go out, he's fast asleep. At least he was a minute ago when I left.
- There, you see, Ralph? You can relax now.
[...]