基本上每个站长都在乎自己的网站的在线率，网站和服务器正常运行时间是商务营利的重要保证，尽量保证网站在线时间，尽快了解到网站和服务器出现问题并解决是很重要的。 如果站点或blog总是离线不能进入的，它将导致访问者心烦并且失去被访问的机会。如果长时间频繁的离线，也可能引起搜索引擎对网站的收录减少。

在这里推荐一些能检测网站在线率的网站，它们中的大部分会以MAIL形式在你的网站无法访问的时候给你提醒。

首先推荐两个国人的，用国人的服务的好处就是最起码不存在语言方面的障碍。

1：www.hkuptime.com
申请地址：http://www.hkuptime.com/register.php
只能免费检测一个网站，频率为60分钟一次。可以检测http ftp  smtp pop等服务。

提供多种在线样式图标以适应网站中插入：
如：
结果演示：http://www.hkuptime.com/598

样式：


2：www.uptime.com.cn
申请地址：http://www.uptime.com.cn/user/register0.asp
可以检测两个网站，频率30分钟一次。可以用他们的短信提醒（收费的）。

提供多种在线样式图标，如果你熟悉JS的话，可以去掉他们的UPTIME.COM.CN字样，呵呵~
演示结果：



结果页：
http://www.uptime.com.cn/general/publicMonthlyReport.asp?ID=358

3：saycoo.com
中文的，不过貌似调用不了。
http://monitor.saycoo.com/publicreport/12040/41006

4：http://www.montastic.com/


其它网站也有这样的服务，不多说了，自己看。

和警告的选择或者通知服务：

1：http://www.siteuptime.com/

1 Monitor
30/60 Minute Checks
Uptime Reports
Public Statistics Page
Alert Failure Limit
Control Panel

2：http://host-tracker.com/

Possibility to receive error notifications both to your Email, ICQ, GTalk or cell-phone via SMS;
Possibility to receive specified (daily, weekly, monthly, quarterly, yearly) reports;
Accumulation of availability statistics with further reporting;
Resource accessibility instant check.
Uptime button;
Distributed monitoring;
Instant site check;
Monitoring period – every 1/5/15/30/60 minutes;
The HEAD/POST/GET HTTP-methods support;
Keyword presence control of a page;

3：http://www.internetvista.com/

Light offer checks and monitors 1 server on HTTP pages every 60 minutes with email alerts

4：http://www.econtrolportal.net
注册：http://www.econtrolportal.net/cgi-bin/ecpnetreg
登陆：http://www.econtrolportal.net/cgi-bin/ecplogin
Free Internet web-based monitoring service provided to promote EControl Portal downloadable software, monitors and watches Internet services such as HTTP, HTTPS, PING, DNS, IMAP, POP3, RADIUS, NNTP, WEB CONTENT and AUTHORIZATION. When it detects that one of your internet services is not responding, it will send notifications to you at all of your designated contacts for that site.

5：http://www.serviceuptime.com/

One monitoring service (any port or service) checked every 30 minutes from servers all over the world.

6：http://www.servermojo.com/

Monitor servers web, ping, dns, mysql and more approximately every 15 minutes. Free notifications by email and via Jabber IM server any time server is not responding, or optionally by SMS notifications for a small monthly fee.

7：http://uppanel.com/

Free website monitoring service that watches your websites and alert you if one becomes unavailable.

8：WebSitePulse
申请：http://www2.websitepulse.com/details.php3?plan=2250

Monitor the performance and status of your website HTTP server for free at interval of 60 minutes with e-mail and cellular phone notifications.

9：http://www.uptrends.com

Free version checks 1 website every 30 minutes and provides detailed reports and alerts by email, RSS or IM.

10：http://basicstate.com/
Free uptime monitoring service monitors http and https services every 15 minutes for unlimited number of sites. Instant trouble alerts by email or SMS (premium fees).