When you think that nobody is watching, be sure that Allaah is watching.
أَلَمْ تَرَ أَنَّ اللَّهَ يَعْلَمُ مَا فِي السَّمَاوَاتِ وَمَا فِي الْأَرْضِ مَا يَكُونُ مِن نَّجْوَى ثَلَاثَةٍ إِلَّا هُوَ رَابِعُهُمْ وَلَا خَمْسَةٍ إِلَّا هُوَ سَادِسُهُمْ وَلَا أَدْنَى مِن ذَلِكَ وَلَا أَكْثَرَ إِلَّا هُوَ مَعَهُمْ أَيْنَ مَا كَانُوا ثُمَّ يُنَبِّئُهُم بِمَا عَمِلُوا يَوْمَ الْقِيَامَةِ إِنَّ اللَّهَ بِكُلِّ شَيْءٍ عَلِيمٌ
"Have you not seen that Allaah knows whatever is in the heavens and whatever is on the earth? There is no secret counsel of three, but He is their fourth (with His Knowledge, while He Himself is over the Throne, over the seventh heaven), nor of five but He is their sixth (with His Knowledge), not of less than that or more, but He is with them (with His Knowledge) wheresoever they may be; and afterwards, on the Day of Resurrection, He will inform them of what they did. Verily, Allaah is the All-Knower of everything." [Surat al-Mujaadilah, 7]