Microcontroller Based Visitor Indicator System using GSM Module with Text Message as Feedback. International Journal of Current Engineering and Technology, [S. l.], v. 4, n. 4, p. 2360–2363, 2014. Disponível em: https://ijcet.evegenis.org/index.php/ijcet/article/view/1042. Acesso em: 13 apr. 2026.