Baby Monitor Problem Using Two At The Same Time

I have two Tomy baby monitor sets, for two kids, and am unable to have both turned on at the same time, as one will screech, as though the one in the childs room is turned off (safety feature).

I can use either set independently, problem is when both children are in bed and I want to listen in on both.

I assume Tomy probably use the same frequency on all their products, which is what is causing this problem.

I was thinking of opening the device up and seeing if there was a frequency adjuster or something, but opening it is not straight forward - I need a special tool, so will have to imporovise.

I bought both on eBay, so dont have a receipt to go back to the shop etc.

Anybody had this problem before?
How did you solve it?

If a special tool is required to open it, you can be sure there is no easy means of adjusting the frequency.
Leo

do they not have an option to select different channels? which is essentially what you are trying to do?

No, that is what I was getting at... I have to open it up to see if there is any way of changing the channel inside, but Leo's comment makes me think otherwise.
I am thinking it is because both are the Tomy brand, maybe I should get one non-Tomy.

We're running a Tomy with an A/B selector on side and a new digital BT model (cost about 70euro in Argos) without issue.

we run two of these digital ones no problem

Had the Tomy ones but buzzing and interference made us upgrade

We had two Tomy monitors a while back, they had little dip switches in the battery compartment to set the channel I think. We did get some interference even setting these.

In the end we stopped using them as the kids kept waking us up.

SSE