That sounds like an odd situation. If you have an open WiFi network, it could be a random camera connecting. I suggest that you change your WiFi's password and don't tell anyone what the new one is.
If you have a mobile phone, download a camera scanning app - it should let you view the camera's feed so you can see where it is. I use https://play.google.com/store/apps/details?id=com.alexvas.dvr