Everyone is different, and there are no universal signals to look out for. Communicating with the partner will help. If you want to use withdrawal for contraception but you are unsure what the signals are, practice with a condom first.
Still not working? If you do not want to get pregnant now and pulling out is not as easy as you thought, you may want to use a more effective method. A few that do not require action while you are having sex are the IUD, the implant, and the injectable. Consider using condoms for STI protection.
Try a different method: implant, IUD, injectable and condoms.
References:
- World Health Organization Department of Reproductive Health and Research and Johns Hopkins Bloomberg School of Public Health Center for Communication Programs (2018) Family Planning: A Global Handbook for Providers. Baltimore and Geneva. Retrieved from https://apps.who.int/iris/bitstream/handle/10665/260156/9780999203705-eng.pdf?sequence=1