How can I check whether the Sim Card is available in an android device?

Use TelephonyManager.

http://developer.android.com/reference/android/telephony/TelephonyManager.html

As Falmarri notes, you will want to use getPhoneType FIRST of all, to see if you are even dealing with a GSM phone. If you are, then you can also get the SIM state.

TelephonyManager telMgr = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
    int simState = telMgr.getSimState();
            switch (simState) {
                case TelephonyManager.SIM_STATE_ABSENT:
                    // do something
                    break;
                case TelephonyManager.SIM_STATE_NETWORK_LOCKED:
                    // do something
                    break;
                case TelephonyManager.SIM_STATE_PIN_REQUIRED:
                    // do something
                    break;
                case TelephonyManager.SIM_STATE_PUK_REQUIRED:
                    // do something
                    break;
                case TelephonyManager.SIM_STATE_READY:
                    // do something
                    break;
                case TelephonyManager.SIM_STATE_UNKNOWN:
                    // do something
                    break;
            }

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EDIT:

Starting at API 26 (Android O Preview) you can query the SimState for individual sim slots by using getSimState(int slotIndex) ie:

int simStateMain = telMgr.getSimState(0);
int simStateSecond = telMgr.getSimState(1);

official documentation

If you’re developing with and older api, you can use TelephonyManager's

String getDeviceId (int slotIndex)
//returns null if device ID is not available. ie. query slotIndex 1 in a single sim device

int devIdSecond = telMgr.getDeviceId(1);

//if(devIdSecond == null)
// no second sim slot available

which was added in API 23 – docs here