Microchip cat flap

[ranoutofquinoaandprosecco]

Do we had one of these fitted at the weekend, before then the cats went in and out when we were in. We moved house a couple of months ago and they had a flap at the old property.
I seem to have not fitted this correctly as I came home today and we had an intruder cat in the house but they obviously couldn't get out as it only scans for my cats microchips.

How do I set it so they can't get in to the house?

What type of flap is it? With mine you dont need a chip to get out but need it to get back in unless you set it to 'in only' on the dial in which case none can leave

Have you put it in the right way round? What controls does it have?

Thanks for the reply, that's what I sort of though too! Doh! Going to have to see if I can turn it around!