Menampilkan Notifikasi saat Menginputkan Data Yang Sama

Assalamualaikum mas.
Saya ada masalah saat input data yang sama tetapi masih bisa input.
Mohon bantuannya mas kalau inputkan NIP sama seharusnya ada notif gagal itu gimana ya?
 
---------------------------------------- Model ---------------------------------------------
<?php
 
function addpegawai($data){
     $this->db->insert('pegawai',$data);
}
 
?>
--------------------------------------- Controller -----------------------------------------
<?php
 
function tambah_pegawai(){
		$this->cek_admin();
		$data['title'] = 'Halaman Tambah Pegawai';
		$data['password'] = $this->Model_pegawai->password();
		$this->template->load('admin/template','admin/mod_pegawai/tambah_pegawai', $data);
}
 
function input_pegawai(){
		$this->cek_admin();
		$nmfile = "PEGAWAI_RSSP_".time();
		$config['upload_path']='./assets/foto_pegawai/';
		$config['allowed_types']='jpg|jpeg|png';
		$config['file_name'] = $nmfile;
		$config['max_size'] = '1000'; // kb
		$this->load->library('upload', $config);
		$this->upload->do_upload('foto');
		$hasil=$this->upload->data();
 
        	$data = array(
				'nip' => $this->input->post('nip'),
				'password' => sha1($this->input->post('password')),
				'nama_lengkap' => $this->input->post('nama_lengkap'),
				'foto' => $hasil['file_name'],
				'tmp_lahir' => $this->input->post('tmp_lahir'),
				'tgl_lahir' => date_format(date_create($this->input->post('tgl_lahir')), 'Y-m-d'),
				'jns_kelamin' => $this->input->post('jns_kelamin'),
				'agama' => $this->input->post('agama'),
				'gol_darah' => $this->input->post('gol_darah'),
				'status_nikah' => $this->input->post('status_nikah'),
				'pstatus' => $this->input->post('pstatus'),
				'blokir' => $this->input->post('blokir'),
				'alamat' => $this->input->post('alamat'),
				'provinsi' => $this->input->post('provinsi'),
				'kodepos' => $this->input->post('kodepos'),
				'email' => $this->input->post('email'),
				'no_tlp' => $this->input->post('no_tlp')
			);
 
			$this->Model_pegawai->addpegawai($data);
 
			if ($data>=1) {
				$this->session->set_flashdata('message', 
					'<div class="alert alert-warning alert-dismissible" role="alert">
	                    <button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">×</span></button>
	                    Data Berhasil di Tambah...!!!
	                </div>'
	            );
				redirect('administrator/tampil_pegawai','refresh');
			}
       else {
				$this->session->set_flashdata('message', 
					'<div class="alert alert-warning alert-dismissible" role="alert">
	                    <button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">×</span></button>
	                    Mohon Maaf NIP sudah Terdaftar...!!!
	                </div>'
	            );
				redirect('administrator/tambah_pegawai','refresh');
			}
}
 
?>