Ref. No. 1008 Alif
In the name of Allah the Most Gracious the most Merciful
The answer to your question is as follows:
It is unlawful to use anything that belongs to others. If you have used your neighbor’s WiFi in the past without his permission, you have a duty to inform him. If you try to compensate him for using his WiFi connection it would be better.
We also advise you to keep your device’s WiFi switched off so that it will not get connected automatically. You must know that using anything belonging to others is Haram and unlawful as mentioned in a Hadith. So you must take full caution when dealing with others.
And Allah knows best
Darul Uloom Waqf Deoband