How to find a stray cat lost somewhere in my home

Question
It appears a stray cat has moved into my home.  I have seen the cat twice and my son has seen it once. No one else in the family has seen it but they have heard it. We have turned the house upside down looking for it.  It comes out at night and cries/moans throughout the house until someone gets out of bed to look and then it seems to disappear into thin air for a few hours only to come back out again with the cries and moans.  Our home is very large (6000+ sq ft) with many rooms, multiple staircases, etc. so it takes some time to locate the source of the cries/moans at night and by the time we find the location, the cat has disappeared.  We have 3 indoor cats (2 Himalayans and a mix) and we know it is not them as the 2 Himalayans sleep in my room and the other is devoted to my daughter and sleeps with her. Also, the noise that comes from this stray is totally unlike any noises the others have ever made.  The 2 in my room look curious when they hear the cries/moans at night as well but don't leave the room to investigate.  Oddly, their behavior is unchanged during the day as though they do not know there is another cat around.  The 2 Himalayans have always been very curious, following neighborhood cats, dogs and raccoons from window to window so I cannot imagine they would just ignore a stranger in the house if they knew where it was.  I have tried putting food out and taking all food away at night in hopes of catching this stray cat.  I assume it must be eating the other cat food sometime during the day and it appears to be using a litter box as we have found no "messes".  Can you suggest anything?  We are not sleeping much at night due to the noise and then the constant late night searches.  Also, I have no idea about the health of this cat and I fear it might cause health problems for our 3 family cats.

Answer
Janice,

This is a tricky situation.

I would borrow some Have-a-Heart live traps from your local humane society or Animal Control office and put some food in them.  The trick is to lay these out at night when your other cats are put up.  It may take a few nights to do this to catch her.  You will also have to take any other food up, so the only food she will have access to is in the traps.

We are assuming she is in season (hence the moaning noises) and has not had a litter of kittens somewhere in your house.

It is amazing how cats can find places in your house you did not even knew existed.

Please let me know how you make out with this.

Best regards... Norm.