Instead of bluetooth you can also easily use wireless tethering.
There is an app called "Qt Mobile Hotspot", which I have found to work quite reliably.

Of course you want at least the WEP encryption provided. The problem is, many modern wireless devices do not support WEP, my workaround is to carry a Edimax ew-7811un around (very cheap, very little wireless dongle), plug it into any device and it will be able to use your WEP network. (Works also for the native N9 hotspot)

WEP is not secure and can be hacked, but because it isn't supported anymore the risk of somebody having a compatible device, the required skills and the urge to hack your hotspot is very negligible.