I need to create a wireless network with no Internet access with a Pi, because I need to communicate to it with an Android smartphone and a laptop, but being the RPi the highest step in the network hierarchy.
I've found -and tried- that I can do an adhoc network, but I am unable to connect to it with the smartphone. The other alternative is creating a Wi-Fi hotspot, with no NAT, but I don't really have a deep knowledge on networks so I'm really lost in which IP adresses I have to set.
I've followed this tutorial, and found it really useful. Could anyone tell me what should I modify from it to make it only local -apart from not doing the NAT?
The Rapsberry Pi 3 has built in Wi-Fi that can serve as an access point. Based on my experience, with the Pi acting as an access point, you should be able to connect to any device, be it Android or not.
The Pi will act as access point and serve as a DHCP daemon, assigning and handling IP addresses to any devices that connect to it. This will be a standalone network and will not be able to share an Internet connection unless you bridge it. Follow this tutorial up until the Internet sharing part: https://www.raspberrypi.org/documentation/configuration/wireless/access-point.md
Also, it would be better to ask this in the Raspberry Pi stack exchange.