def get_decisive_snr(snrs):
    """Return the SNR for the trigger that decides if an event is detectable.

    If there are two or more detectors, then the decisive SNR is the SNR of the
    second loudest detector (since a coincidence of two or more events is
    required). If there is only one detector, then the decisive SNR is just the
    SNR of that detector. If there are no detectors, then 0 is returned.

    Parameters
    ----------
    snrs : list
        List of SNRs (floats).

    Returns
    -------
    decisive_snr : float

    """
    if len(snrs) > 1:
        return sorted(snrs)[-2]
    elif len(snrs) == 1:
        return snrs[0]
    else:
        return 0.0
