Nguyen, K.-N. ., Nguyen, C.-N., Bui, H.-D., Tran, M.-T. ., Lam, C.-N. ., Truong, Q. B., Nguyen, H. D. and Nguyen, C. N. (2023) “Design of a smart doorbell for a leader’s office with availability status notification and visitor recognition features”, CTU Journal of Innovation and Sustainable Development , 15(2), pp. 28-34. doi: 10.22144/ctu.jen.2023.017.