Искандер,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script>
var otvmas=[15,25,36,87];
function Spisok() {
var Sign = "";
for(var n=0; n<otvmas.length; n++){
Sign += "<option value="+ (n + 1)+">"+otvmas[n]+"</option>";
}
document.getElementById('menu1').options.length = 0;
document.getElementById('menu1').insertAdjacentHTML('beforeEnd',Sign)
}
</script>
</head>
<body>
<form name="vibor" method="post">
<input type="number" min="1" max="255" step="1" value="1" id="nomSign" /><br>
<input type="button" value="Выбор сигнализатора" id="txt" onclick="VoborSign()"/><br>
<input type="button" value="Обновление списка сигнализаторов" id="txt1" onclick="Spisok()"/><br>
</form>
<form >
<select name=ZavN size=1 id="menu1">
</select>
</form>
</body>
</html>