ABSTRAKSI: Seiring berkembangnya kemajuan teknologi, PT Telkom selaku penyedia layanan wireline phone pun mengikuti perkembangan dengan menggelar jaringan Fiber Optik dari sentral sampai rumah kabel. Untuk itu dibutuhkan perangkat bernama Outdoor Multi-Service Access Node (MSAN) sebagai perantara dari fiber optic dari sentral ke rumah kabel. Namun, perangkat tersebut masih memiliki keterbatasanseperti Outdoor MSAN yang sering padam karenagangguan pada internal PLN, pemadaman bergilir, atau pulsa listrik PLN pra-bayar yang habis tanpa pemberitahuan. Warning alarm sebenarnya telah dibuat, tapi ternyata masih ada keterbatasan di sisi radius alarm. Adapun proyek akhir ini membuat rancang bangun dan merealisasikan warning alarm monitoring catu daya PLN dengan SMS Gateway sehingga site engineer tidak perlu standby di kantor. Saat outdoor msan padam, relay akan terbuka dan mengirim tegangan ke alarm console. Tegangan itu dibaca oleh mikrokontroller, lalu memberi perintah pada gsm module untuk memberi warning alarm sesuai program yang dibuat berupa sms ke site engineerdimanapun dia berada. Saat outdoor MSAN menyala kembali, site engineer akan mendapatkan sms pemberitahuan lagi bahwa outdoor MSAN sudah menyala. Warning alarm ini adalah prototype yang menggunakan rangkaian simulasi untuk memonitor 4 outdoor MSAN. Dari hasil pengujian, didapatkan bahwa warning alarm dapat diimplementasikan dengan didapatkan rata-rata tegangan catu daya mikrokontroller yang stabil pada 4.975 v, tegangan catu daya rangkaian simulator yang stabil pada keluaran 4.946 Volt, tegangan yang dihasilkan pada blok rangkaian serial adalah 4.979 Volt, Rata-rata alarm standby time sebesar 67.23 s, Rata-rata alarm time process sebesar 6.453 s, Rata-rata time process for simultaneous detection sebesar 52.52 s. Tapi pada pengujian real belum berhasil karena hanya 5 kali berhasil dalam 30 kali percobaanKata Kunci : multi-service access node, mikrokontroler, SMS gateway, warning alarm, catu daya.ABSTRACT: As the development of technology advances, PT. Telkom as the wireline phone service provider have to follow the update and build optic fiber networks from the central to the home wiring. So, they need a device called outdoorMulti-Service Access Nodeor MSAN. Unfortunately, it still hasa weakness which is the power cut because of the PLN itself, rolling blackouts, or running out of pre-paid power without notice. Actually, an alarm warning had been made but it’s a short range alarm. This final project is to make a design and realization of alarm warning of outdoor MSAN power supply based on microcontroller with SMS gateway so the site engineer don’t have to standby all time in the office. When the outdoor MSAN goes off, the contact of relay will open and give voltage to alarm console. Then, it will read by microcontroller. Next, it will give order to GSM module to give alarm warning via SMS based on the program created. When the power is on, the site engineer will get notification again via SMS that the outdoor MSAN is on. The alarm warning is a prototype that uses a simulation circuit. It will monitor 4 outdoor MSAN. From experiment results, the warning alarm is useful with the voltage in microcontroller’s power supply that is stable at 4.975 v, the voltage in simulator’s power supply that is stable at 4.949 v, the voltage in serial circuit that is stable at 4.979 v, alarm standby time experiments rates at 67.23 s, alarm time process experiments rates at 6.453 s, time process for simultaneous detection experiments experiments rates at 52.52 s. But, the warning alarm’s real condition experiments is unsuccessful because from 30 times test, only 5 test were successful.Keyword: multi-service access node, microkontroller, SMS gateway, warning alarm, power supply